patch 8.2.0035: saving and restoring called_emsg is clumsy

Problem:    Saving and restoring called_emsg is clumsy.
Solution:   Count the number of error messages.
diff --git a/src/ex_cmds2.c b/src/ex_cmds2.c
index 9a31887..4f8f7fb 100644
--- a/src/ex_cmds2.c
+++ b/src/ex_cmds2.c
@@ -167,7 +167,7 @@
 	    // the current scope, such as being inside a try/catch.
 	    timer_busy = timer_busy > 0 || vgetc_busy > 0;
 	    vgetc_busy = 0;
-	    called_emsg = FALSE;
+	    called_emsg = 0;
 	    did_emsg = FALSE;
 	    did_uncaught_emsg = FALSE;
 	    must_redraw = 0;