Slightly improved error messages when love.graphics.newShader fails

src/modules/graphics/opengl/wrap_Graphics.cpp

@@ -505,8 +505,6 @@ int w_newShader(lua_State *L)
 	if (!Shader::isSupported())
 		return luaL_error(L, "Sorry, your graphics card does not support shaders.");
 
-	try
-	{
 	// clamp stack to 2 elements
 	lua_settop(L, 2);
 
@@ -535,10 +533,22 @@ int w_newShader(lua_State *L)
 		sources[Shader::TYPE_FRAGMENT] = fragcode;
 	}
 
+	if (sources.empty())
+	{
+		// Original args had source code, but effectCodeToGLSL couldn't translate it
+		for (int i = 1; i <= 2; i++)
+		{
+			if (lua_isstring(L, i))
+				return luaL_argerror(L, i, "invalid or incomplete shader code");
+		}
+	}
+
+	try
+	{
 		Shader *shader = instance->newShader(sources);
 		luax_newtype(L, "Shader", GRAPHICS_SHADER_T, (void *)shader);
 	}
-	catch(const love::Exception &e)
+	catch (const love::Exception &e)
 	{
 		// memory is freed in Graphics::newShader
 		luax_getfunction(L, "graphics", "_transformGLSLErrorMessages");