virQEMUCapsNewBinary: Avoid NULL dereference

Even with GLib it is still possible for virQEMUCapsNew() to
return NULL because it calls virQEMUCapsInitialize() which is a
wrapper over pthread_once() which may fail. At least, we still
check for its retval. If it so happens that the virQEMUCapsNew()
fails and returns NULL, we should not dereference it.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>
Reviewed-by: NDaniel P. Berrangé <berrange@redhat.com>

src/qemu/qemu_capabilities.c

@@ -1713,7 +1713,8 @@ virQEMUCapsNewBinary(const char *binary)
 {
     virQEMUCapsPtr qemuCaps = virQEMUCapsNew();
 
-    qemuCaps->binary = g_strdup(binary);
+    if (qemuCaps)
+        qemuCaps->binary = g_strdup(binary);
 
     return qemuCaps;
 }