validate: Fix memory leaks when context parse fails

When g_option_context_parse fails, context and error variables are not getting free'd
which results in memory leaks. Free'ing the same.

And replacing g_error_free with g_clear_error, which checks if the error being passed
is not NULL and sets the variable to NULL on free'ing.

https://bugzilla.gnome.org/show_bug.cgi?id=753862

validate/tools/gst-validate-images-check.c

@@ -75,6 +75,7 @@ main (int argc, char **argv)
   if (!g_option_context_parse (ctx, &argc, &argv, &err)) {
     g_printerr ("Error initializing: %s\n", err->message);
     g_option_context_free (ctx);
+    g_clear_error (&err);
     return -1;
   }
 

validate/tools/gst-validate-media-check.c

@@ -79,6 +79,7 @@ main (int argc, gchar ** argv)
   if (!g_option_context_parse (ctx, &argc, &argv, &err)) {
     g_printerr ("Error initializing: %s\n", err->message);
     g_option_context_free (ctx);
+    g_clear_error (&err);
     exit (1);
   }
 

validate/tools/gst-validate-transcoding.c

@@ -873,6 +873,7 @@ main (int argc, gchar ** argv)
   if (!g_option_context_parse (ctx, &argc, &argv, &err)) {
     g_printerr ("Error initializing: %s\n", err->message);
     g_option_context_free (ctx);
+    g_clear_error (&err);
     exit (1);
   }
 

validate/tools/gst-validate.c

@@ -136,7 +136,7 @@ bus_callback (GstBus * bus, GstMessage * message, gpointer data)
       if (debug)
         g_print ("Additional debug info:\n%s\n", debug);
 
-      g_error_free (gerror);
+      g_clear_error (&gerror);
       g_free (debug);
       g_free (name);
       break;