Background rendering didn't work anymore!

- STUPID mistake from me in setting the waitcursor...
- icons for UI got freed, without checking if it existed (crash in end)
- call to close mainwindow didn't check if window existed

note:
I usually test the "blender -b" case, which should start blender,
initialize all, free all, and print "blender quit" to signal all is fine.

source/blender/blenkernel/intern/icons.c

@@ -50,7 +50,7 @@
 
 /* GLOBALS */
 
-static GHash* gIcons = 0;
+static GHash* gIcons = NULL;
 
 static int gNextIconId = 1;
 
@@ -106,8 +106,9 @@ void BKE_icons_init(int first_dyn_id)
 
 void BKE_icons_free()
 {
-	BLI_ghash_free(gIcons, 0, icon_free);
-	gIcons = 0;
+	if(gIcons)
+		BLI_ghash_free(gIcons, 0, icon_free);
+	gIcons = NULL;
 }
 
 

source/blender/src/editscreen.c

@@ -154,10 +154,12 @@ static void screen_set_cursor(bScreen *sc)
 
 void waitcursor(int val)
 {
-	if(val) {
-		set_cursor(CURSOR_WAIT);
-	} else {
-		screen_set_cursor(G.curscreen);
+	if(G.curscreen) {
+		if(val) {
+			set_cursor(CURSOR_WAIT);
+		} else {
+			screen_set_cursor(G.curscreen);
+		}
 	}
 }
 
@@ -1481,7 +1483,8 @@ void screenmain(void)
 
 #if 0
 //#ifdef _WIN32	// FULLSCREEN
-void mainwindow_toggle_fullscreen(int fullscreen){
+void mainwindow_toggle_fullscreen(int fullscreen)
+{
 	if (fullscreen) U.uiflag |= USER_FLIPFULLSCREEN;
 	else U.uiflag &= ~USER_FLIPFULLSCREEN;
 
@@ -1489,20 +1492,27 @@ void mainwindow_toggle_fullscreen(int fullscreen){
 }
 #endif
 
-void mainwindow_raise(void) {
-	window_raise(mainwin);
+void mainwindow_raise(void) 
+{
+	if(mainwin)
+		window_raise(mainwin);
 }
 
-void mainwindow_make_active(void) {
-	window_make_active(mainwin);
+void mainwindow_make_active(void) 
+{
+	if(mainwin)
+		window_make_active(mainwin);
 }
 
-void mainwindow_close(void) {
-	window_destroy(mainwin);
+void mainwindow_close(void) 
+{
+	if(mainwin)
+		window_destroy(mainwin);
 	mainwin= NULL;
 }
 
-void mainwindow_set_filename_to_title(char *filename) {
+void mainwindow_set_filename_to_title(char *filename)
+{
 	char str[FILE_MAXDIR + FILE_MAXFILE];
 	char dir[FILE_MAXDIR];
 	char file[FILE_MAXFILE];