b=616360; add missing return in WebGL RenderbufferStorage; r=bjacob, a=b

content/canvas/src/WebGLContextGL.cpp

@@ -2695,7 +2695,7 @@ WebGLContext::RenderbufferStorage(WebGLenum target, WebGLenum internalformat, We
         internalformatForGL = LOCAL_GL_DEPTH24_STENCIL8;
         break;
     default:
-        ErrorInvalidEnumInfo("renderbufferStorage: internalformat", internalformat);
+        return ErrorInvalidEnumInfo("renderbufferStorage: internalformat", internalformat);
     }
 
     gl->fRenderbufferStorage(target, internalformatForGL, width, height);