patch 9.0.0750: crash when popup closed in callback

Problem:    Crash when popup closed in callback. (Maxim Kim)
Solution:   In syntax_end_parsing() check that syn_block is valid.

src/drawscreen.c

@@ -2486,7 +2486,7 @@ win_update(win_T *wp)
 		// Let the syntax stuff know we skipped a few lines.
 		if (syntax_last_parsed != 0 && syntax_last_parsed + 1 < lnum
 						       && syntax_present(wp))
-		    syntax_end_parsing(syntax_last_parsed + 1);
+		    syntax_end_parsing(wp, syntax_last_parsed + 1);
 #endif
 
 		// Display one line.
@@ -2601,7 +2601,7 @@ win_update(win_T *wp)
 #ifdef FEAT_SYN_HL
     // Let the syntax stuff know we stop parsing here.
     if (syntax_last_parsed != 0 && syntax_present(wp))
-	syntax_end_parsing(syntax_last_parsed + 1);
+	syntax_end_parsing(wp, syntax_last_parsed + 1);
 #endif
 
     // If we didn't hit the end of the file, and we didn't finish the last

src/proto/syntax.pro

@@ -2,7 +2,7 @@
 void syntax_start(win_T *wp, linenr_T lnum);
 void syn_stack_free_all(synblock_T *block);
 void syn_stack_apply_changes(buf_T *buf);
-void syntax_end_parsing(linenr_T lnum);
+void syntax_end_parsing(win_T *wp, linenr_T lnum);
 int syntax_check_changed(linenr_T lnum);
 int get_syntax_attr(colnr_T col, int *can_spell, int keep_state);
 void syntax_clear(synblock_T *block);

src/syntax.c

@@ -1542,10 +1542,12 @@ syn_stack_equal(synstate_T *sp)
  * lnum ->  line below window
  */
     void
-syntax_end_parsing(linenr_T lnum)
+syntax_end_parsing(win_T *wp, linenr_T lnum)
 {
     synstate_T	*sp;
 
+    if (syn_block != wp->w_s)
+	return;  // not the right window
     sp = syn_stack_find_entry(lnum);
     if (sp != NULL && sp->sst_lnum < lnum)
 	sp = sp->sst_next;

src/version.c

@@ -695,6 +695,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    750,
 /**/
     749,
 /**/