glsl_restart: Stop segfaulting

Using git bisect, e497a08 introduces a
window where globalUBOProxy can be null after glsl_restart. Therefore,
also return early, if glboalUBOProxy is null. It will be instantiated
later.

Further, only initialize world shaders *AFTER* all shader storage has
been initialized.

Author: DolceTriade

src/engine/renderer/tr_backend.cpp

@@ -2830,7 +2830,7 @@ static void RB_RenderPostProcess()
 
 static void SetFrameUniforms() {
 	// This can happen with glsl_restart/vid_restart in R_SyncRenderThread()
-	if ( !stagingBuffer.Active() ) {
+	if ( !stagingBuffer.Active() || globalUBOProxy == nullptr ) {
 		return;
 	}
 

src/engine/renderer/tr_shade.cpp

@@ -256,11 +256,6 @@ static void GLSL_InitGPUShadersOrError()
 		gl_depthReductionShader->MarkProgramForBuilding();
 	}
 
-	if ( tr.world ) // this only happens with /glsl_restart
-	{
-		GLSL_InitWorldShaders();
-	}
-
 	if ( glConfig.realtimeLighting )
 	{
 		gl_shaderManager.LoadShader( gl_depthtile1Shader );
@@ -384,6 +379,12 @@ static void GLSL_InitGPUShadersOrError()
 	gl_shaderManager.PostProcessGlobalUniforms();
 	gl_shaderManager.InitShaders();
 
+	// Init world shaders last so that everyhthing is already initialized.
+	if ( tr.world ) // this only happens with /glsl_restart
+	{
+		GLSL_InitWorldShaders();
+	}
+
 	if ( r_lazyShaders.Get() == 0 )
 	{
 		gl_shaderManager.BuildAll( false );