patch 9.0.0282: a nested timout stops the previous timeout

Problem:    A nested timout stops the previous timeout.
Solution:   Ignore any nested timeout.
diff --git a/src/evalfunc.c b/src/evalfunc.c
index a5f9ee3..d2cc8fc 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -9176,7 +9176,8 @@
 
 theend:
 #ifdef FEAT_RELTIME
-    disable_regexp_timeout();
+    if (time_limit > 0)
+	disable_regexp_timeout();
 #endif
     vim_free(pat2);
     vim_free(pat3);