Reviewed shader loading message

Author: raysan5

examples/shaders/shaders_model_shader.c

@@ -57,7 +57,7 @@ int main(void)
     // NOTE: Defining 0 (NULL) for vertex shader forces usage of internal default vertex shader
     Shader shader = LoadShader(0, TextFormat("resources/shaders/glsl%i/grayscale.fs", GLSL_VERSION));
 
-    model.materials[0].shader = shader;                     // Set shader effect to 3d model
+    model.materials[0].shader = shader;                 // Set shader effect to 3d model
     model.materials[0].maps[MATERIAL_MAP_DIFFUSE].texture = texture; // Bind texture to model
 
     Vector3 position = { 0.0f, 0.0f, 0.0f };    // Set model position

src/rcore.c

@@ -1315,6 +1315,8 @@ Shader LoadShader(const char *vsFileName, const char *fsFileName)
     if (vsFileName != NULL) vShaderStr = LoadFileText(vsFileName);
     if (fsFileName != NULL) fShaderStr = LoadFileText(fsFileName);
 
+    if ((vShaderStr == NULL) && (fShaderStr == NULL)) TraceLog(LOG_WARNING, "SHADER: Shader files provided are not valid, using default shader");
+    
     shader = LoadShaderFromMemory(vShaderStr, fShaderStr);
 
     UnloadFileText(vShaderStr);