[librsvg] rsvg_decode_data_uri(): Restore ability to pass a null out_mime_type

[Federico Mena Quintero <federico src gnome org>]

commit aeb168ae1b7bbecb31cca5dca162bcb6d9938791
Author: Federico Mena Quintero <federico gnome org>
Date:   Sun Nov 18 16:53:03 2018 -0600

    rsvg_decode_data_uri(): Restore ability to pass a null out_mime_type
    
    Merge request !153 was due to a bug when calling
    rsvg_decode_data_uri() with out_mime_type=NULL.  This was allowed in
    the pre-rustification version of that function.  This commit restores
    that behavior, and adds a test for
    
      <xi:include href="data:text/xml,&lt;xml...">
    
    since the tests were not hitting that code path, which contained the crash.

 rsvg_internals/src/io.rs                   | 11 ++++++++---
 tests/fixtures/crash/xinclude-text-xml.svg | 28 ++++++++++++++++++++++++++++
 2 files changed, 36 insertions(+), 3 deletions(-)
---
diff --git a/rsvg_internals/src/io.rs b/rsvg_internals/src/io.rs
index d534ae2e..37963b58 100644
--- a/rsvg_internals/src/io.rs
+++ b/rsvg_internals/src/io.rs
@@ -32,14 +32,16 @@ pub fn rsvg_decode_data_uri(
     error: *mut *mut glib_sys::GError,
 ) -> *mut libc::c_char {
     unsafe {
-        assert!(!out_mime_type.is_null());
         assert!(!out_size.is_null());
 
         let uri = utf8_cstr(uri);
 
         match decode_data_uri(uri) {
             Ok(binary_data) => {
-                *out_mime_type = binary_data.content_type.to_glib_full();
+                if !out_mime_type.is_null() {
+                    *out_mime_type = binary_data.content_type.to_glib_full();
+                }
+
                 *out_size = binary_data.data.len();
 
                 if !error.is_null() {
@@ -51,7 +53,10 @@ pub fn rsvg_decode_data_uri(
             }
 
             Err(_) => {
-                *out_mime_type = ptr::null_mut();
+                if !out_mime_type.is_null() {
+                    *out_mime_type = ptr::null_mut();
+                }
+
                 *out_size = 0;
 
                 set_gerror(error, 0, "could not decode data: URL");
diff --git a/tests/fixtures/crash/xinclude-text-xml.svg b/tests/fixtures/crash/xinclude-text-xml.svg
new file mode 100644
index 00000000..3222b6c1
--- /dev/null
+++ b/tests/fixtures/crash/xinclude-text-xml.svg
@@ -0,0 +1,28 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<svg version="1.1"
+     xmlns="http://www.w3.org/2000/svg";
+     xmlns:xi="http://www.w3.org/2001/XInclude";
+     width="16"
+     height="16">
+  <style type="text/css">
+    rect,circle,path {
+      fill: rgb(0,255,0) !important;
+    }
+    .warning {
+      fill: rgb(0,255,0) !important;
+    }
+    .error {
+      fill: rgb(0,255,0) !important;
+    }
+    .success {
+      fill: rgb(255,0,0) !important;
+    }
+  </style>
+  <xi:include href="data:text/xml,&lt;svg xmlns=&quot;http://www.w3.org/2000/svg&quot; width=&quot;16&quot; 
height=&quot;16&quot;&gt;
+    &lt;g color=&quot;#bebebe&quot; font-weight=&quot;400&quot; fill=&quot;#474747&quot;&gt;
+        &lt;path d=&quot;M1.75 4C.798 4 0 4.798 0 5.75v4.5C0 11.202.798 12 1.75 12h.125l-.781 1.563L.375 
15h9.25l-.719-1.437L8.125 12h.125c.952 0 1.75-.798 1.75-1.75v-4.5C10 4.798 9.202 4 8.25 4zM2 6h6v4H2z&quot; 
style=&quot;line-height:normal;-inkscape-font-specification:Sans;text-indent:0;text-align:start;text-decoration-line:none;text-transform:none;marker:none&quot;
 font-family=&quot;Sans&quot; overflow=&quot;visible&quot;/&gt;
+        &lt;path d=&quot;M7.75 1C6.798 1 6 1.798 6 2.75V3h8v4h-3v3.25c0 .66-.252 1.27-.656 
1.75h5.28l-1.5-3h.126C15.202 9 16 8.202 16 7.25v-4.5C16 1.798 15.202 1 14.25 1z&quot; 
style=&quot;line-height:normal;text-indent:0;text-align:start;text-decoration-line:none;text-transform:none;marker:none&quot;
 font-family=&quot;Andale Mono&quot; overflow=&quot;visible&quot;/&gt;
+    &lt;/g&gt;
+&lt;/svg&gt;
+"/>
+</svg>