Silence GCC warnings in non debug mode building

[darix]

diff --git a/ext/yajl/yajl_ext.c b/ext/yajl/yajl_ext.c
index 97a052c..18dca25 100644
--- a/ext/yajl/yajl_ext.c
+++ b/ext/yajl/yajl_ext.c
@@ -885,6 +885,8 @@ static VALUE rb_yajl_projector_build_simple_value(yajl_event_stream_t parser, ya

         default:;
             assert(0);
+            // silence gcc error handling
+            return Qnil;
     }
 }

@@ -923,6 +925,8 @@ static VALUE rb_yajl_projector_build_string(yajl_event_stream_t parser, yajl_eve

         default:; {
             assert(0);
+            // silence gcc error handling
+            return Qnil;
         }
     }
 }