Reapply "dont call I_Quit from withing quit_handler, let it signal main loop to quit"

This reverts commit 8156c6e210.

src/d_main.cpp

@@ -991,6 +991,9 @@ void D_SRB2Loop(void)
 
 	for (;;)
 	{
+		if (I_Interrupted())
+			I_Quit();
+
 		precise_t enterprecise = I_GetPreciseTime();
 
 		memset(&g_dc, 0, sizeof(g_dc));

src/i_system.h

@@ -288,6 +288,8 @@ INT32 I_StartupSystem(void);
 */
 void I_ShutdownSystem(void);
 
+boolean I_Interrupted(void);
+
 /**	\brief	The I_GetDiskFreeSpace function
 
 	\param	freespace	a INT64 pointer to hold the free space amount

src/sdl/i_system.cpp

@@ -525,11 +525,19 @@ FUNCNORETURN static ATTRNORETURN void signal_handler(INT32 num)
 }
 #endif
 
-FUNCNORETURN static ATTRNORETURN void quit_handler(int num)
+static volatile sig_atomic_t interrupted = 0;
+
+boolean I_Interrupted(void)
+{
+	return interrupted;
+}
+
+static void quit_handler(int num)
 {
 	signal(num, SIG_DFL); //default signal action
 	raise(num);
-	I_Quit();
+	//I_Quit();
+	interrupted = true;
 }
 
 #ifdef HAVE_TERMIOS

src/sdl/i_video.cpp

@@ -1839,7 +1839,8 @@ void I_ShutdownGraphics(void)
 		SDL_GL_DeleteContext(sdlglcontext);
 	}
 #endif
-	SDL_QuitSubSystem(SDL_INIT_VIDEO);
+	if (SDL_WasInit(SDL_INIT_VIDEO) == SDL_INIT_VIDEO)
+		SDL_QuitSubSystem(SDL_INIT_VIDEO);
 	framebuffer = SDL_FALSE;
 }