goom: possible uninitialized variables warning

Build fails with the latest snapshot of gcc-4.9 because param1 and param2 might
possibly be used uninitialized. They are set depending on the cases of a switch
statement and the compiler sees this as not a complete guarantee.
Set them to 0 if the switch statement falls down to the default case.

https://bugzilla.gnome.org/show_bug.cgi?id=750566#c6

gst/goom/goom_core.c

@@ -847,6 +847,9 @@ choose_a_goom_line (PluginInfo * goomInfo, float *param1, float *param2,
         *amplitude = 1.5f;
       }
       break;
+    default:
+      *param1 = *param2 = 0;
+      break;
   }
 
   *couleur = goom_irand (goomInfo->gRandom, 6);