[yelp] Check the strstr() return value before using it

[David King <davidk src gnome org>]

commit 9847b4320718f5a2f0f61b4142268d6f3e273f6f
Author: Tomas Popela <tpopela redhat com>
Date:   Mon Jul 23 11:56:21 2018 +0200

    Check the strstr() return value before using it
    
    yelp-3.28.1/libyelp/yelp-uri-builder.c:81: returned_null: "strstr" returns null (checked 10 out of 12 
times).
    yelp-3.28.1/libyelp/yelp-uri-builder.c:81: var_assigned: Assigning: "resource" = null return value from 
"strstr".
    yelp-3.28.1/libyelp/yelp-uri-builder.c:82: dereference: Incrementing a pointer which might be null: 
"resource".

 libyelp/yelp-uri-builder.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)
---
diff --git a/libyelp/yelp-uri-builder.c b/libyelp/yelp-uri-builder.c
index bb34d202..58a53ac9 100644
--- a/libyelp/yelp-uri-builder.c
+++ b/libyelp/yelp-uri-builder.c
@@ -78,9 +78,10 @@ build_yelp_uri (const gchar *uri_str)
   memmove (uri, uri + BOGUS_PREFIX_LEN, strlen (uri) - BOGUS_PREFIX_LEN + 1);
 
   /* Remove the leading slash */
-  resource = strstr (uri, ":");
-  resource++;
-  memmove (resource, resource + 1, strlen (resource));
+  if ((resource = strstr (uri, ":"))) {
+    resource++;
+    memmove (resource, resource + 1, strlen (resource));
+  }
 
   /* Remove the trailing slash if any */
   path_len = strlen (uri);