epoxy_internal_has_gl_extension, epoxy_egl_version: add some missing …

…nullpointer checks from https://bugzilla.redhat.com/show_bug.cgi?id=1395366

Related commit: b3b8bd9
 Fix "epoxy_glx_version" to handle the case when GLX is not active on the display.
Patch is tweak from the original version posted by Tom Horsley

src/dispatch_common.c

@@ -478,6 +478,7 @@ epoxy_internal_has_gl_extension(const char *ext, bool invalid_op_mode)
 
         for (i = 0; i < num_extensions; i++) {
             const char *gl_ext = (const char *)glGetStringi(GL_EXTENSIONS, i);
+            if(! gl_ext) return false;
             if (strcmp(ext, gl_ext) == 0)
                 return true;
         }

src/dispatch_egl.c

@@ -62,12 +62,16 @@ epoxy_egl_version(EGLDisplay dpy)
 {
     int major, minor;
     const char *version_string;
-    int ret;
+    int ret=0, sscanf_ret;
 
-    version_string = eglQueryString(dpy, EGL_VERSION);
-    ret = sscanf(version_string, "%d.%d", &major, &minor);
-    assert(ret == 2);
-    return major * 10 + minor;
+    if ((version_string = eglQueryString(dpy, EGL_VERSION)))
+    {
+        sscanf_ret = sscanf(version_string, "%d.%d", &major, &minor);
+        assert(sscanf_ret == 2);
+        ret = major * 10 + minor;
+    }
+
+    return ret;
 }
 
 bool