[gparted] Accept NUL as a valid UTF-8 character again (#136)

[Curtis Gedak <gedakc src gnome org>]

commit 7dbf0691f17a86190ad557467c393b80ba661527
Author: Mike Fleetwood <mike fleetwood googlemail com>
Date:   Sat Feb 20 23:56:28 2021 +0000

    Accept NUL as a valid UTF-8 character again (#136)
    
    On newer distributions the PipeCapture tests have been failing like
    this:
        $ ./test_PipeCapture
        ...
        [ RUN      ] PipeCaptureTest.ReadEmbeddedNULCharacter
        test_PipeCapture.cc:336: Failure
              Expected: inputstr
             Of length: 6
        To be equal to: capturedstr.raw()
             Of length: 5
        With first binary difference:
        < 0x00000000  "ABC.EF"            41 42 43 00 45 46
        --
        > 0x00000000  "ABCEF"             41 42 43 45 46
        [  FAILED  ] PipeCaptureTest.ReadEmbeddedNULCharacter (0 ms)
        [ RUN      ] PipeCaptureTest.ReadNULByteInMiddleOfMultiByteUTF8Character
        test_PipeCapture.cc:353: Failure
              Expected: expectedstr
             Of length: 7
        To be equal to: capturedstr.raw()
             Of length: 6
        With first binary difference:
        < 0x00000000  "._45678"           00 5F 34 35 36 37 38
        --
        > 0x00000000  "_45678"            5F 34 35 36 37 38
        [  FAILED  ] PipeCaptureTest.ReadNULByteInMiddleOfMultiByteUTF8Character (0 ms)
        ...
    
    Found that test_PipeCapture succeeds on Fedora 31 and fails on
    Fedora 32.  Also test_PipeCapture binary from Fedora 31 and 32 both pass
    on Fedora 31 and both fail on Fedora 32.  So something outside of the
    GParted code and tests is the cause.
    
    Confirmed that this GLib change "Add a missing check to
    g_utf8_get_char_validated()" [1], first released in GLib 2.63.0, made
    the difference.  On Fedora 32 with GLib 2.64.6, rebuilt GLib with that
    change reverted and the tests passed.  Anyway fix the wrapper GParted
    has around g_utf8_get_char_validated() to also handle this case of
    reading a NUL character.
    
    [1] https://gitlab.gnome.org/GNOME/glib/-/commit/568720006cd1da3390c239915337ed0a56a23f2e
        Add a missing check to g_utf8_get_char_validated()
    
    Closes #136 - 1.2.0: test suite is failing in test_PipeCapture

 src/PipeCapture.cc | 4 ++++
 1 file changed, 4 insertions(+)
---
diff --git a/src/PipeCapture.cc b/src/PipeCapture.cc
index d5b6f4f2..3244123a 100644
--- a/src/PipeCapture.cc
+++ b/src/PipeCapture.cc
@@ -260,6 +260,10 @@ gunichar PipeCapture::get_utf8_char_validated(const char *p, gssize max_len)
        gunichar uc = g_utf8_get_char_validated(p, max_len);
        if (uc == UTF8_PARTIAL && max_len > 0)
        {
+               // Report NUL character as such.
+               if (*p == '\0')
+                       return '\0';
+
                // If g_utf8_get_char_validated() found a NUL byte in the middle of a
                // multi-byte character, even when there are more bytes available as
                // specified by max_len, it reports a partial UTF-8 character.  Report