setShader errors on compute shaders;

src/graphics/graphics.c

@@ -303,6 +303,7 @@ Shader* lovrGraphicsGetShader() {
 }
 
 void lovrGraphicsSetShader(Shader* shader) {
+  lovrAssert(!shader || lovrShaderGetType(shader) == SHADER_GRAPHICS, "Compute shaders can not be set as the active shader");
   lovrRetain(shader);
   lovrRelease(state.pipelines[state.pipeline].shader);
   state.pipelines[state.pipeline].shader = shader;