patch 8.1.1492: MS-Windows: when "!" is in 'guioptions' ":!start" fails

Problem:    MS-Windows: when "!" is in 'guioptions' ":!start" fails.
Solution:   Do not use a terminal window when the shell command begins with
            "!start". (Yasuhiro Matsumoto, closes #4504)

src/misc2.c

@@ -3251,7 +3251,11 @@ call_shell(char_u *cmd, int opt)
 	/* The external command may update a tags file, clear cached tags. */
 	tag_freematch();
 
-	if (cmd == NULL || *p_sxq == NUL)
+	if (cmd == NULL || *p_sxq == NUL
+#if defined(FEAT_GUI_MSWIN) && defined(FEAT_TERMINAL)
+		|| vim_strchr(p_go, GO_TERMINAL) != NULL
+#endif
+		)
 	    retval = mch_call_shell(cmd, opt);
 	else
 	{

src/os_win32.c

@@ -4640,7 +4640,7 @@ mch_call_shell(
     }
 #endif
 #if defined(FEAT_GUI) && defined(FEAT_TERMINAL)
-    /* TODO: make the terminal window work with input or output redirected. */
+    // TODO: make the terminal window work with input or output redirected.
     if (
 # ifdef VIMDLL
 	    gui.in_use &&
@@ -4648,13 +4648,23 @@ mch_call_shell(
 	    vim_strchr(p_go, GO_TERMINAL) != NULL
 	 && (options & (SHELL_FILTER|SHELL_DOOUT|SHELL_WRITE|SHELL_READ)) == 0)
     {
-	/* Use a terminal window to run the command in. */
+	char_u	*cmdbase = cmd;
+
+	// Skip a leading quote and (.
+	while (*cmdbase == '"' || *cmdbase == '(')
+	    ++cmdbase;
+
+	// Check the command does not begin with "start "
+	if (STRNICMP(cmdbase, "start", 5) != 0 || !VIM_ISWHITE(cmdbase[5]))
+	{
+	    // Use a terminal window to run the command in.
 	    x = mch_call_shell_terminal(cmd, options);
 # ifdef FEAT_TITLE
 	    resettitle();
 # endif
 	    return x;
 	}
+    }
 #endif
 
     /*

src/version.c

@@ -767,6 +767,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1492,
 /**/
     1491,
 /**/