patch 8.2.1820: Vim9: crash when error happens in timer callback

Problem:    Vim9: crash when error happens in timer callback.
Solution:   Check that current_exception is not NULL. (closes #7100)

src/ex_docmd.c

@@ -1234,6 +1234,10 @@ do_cmdline(
 
     if (trylevel == 0)
     {
+	// Just in case did_throw got set but current_exception wasn't.
+	if (current_exception == NULL)
+	    did_throw = FALSE;
+
 	/*
 	 * When an exception is being thrown out of the outermost try
 	 * conditional, discard the uncaught exception, disable the conversion

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1820,
 /**/
     1819,
 /**/