patch 8.2.5128: syntax disabled when using synID() in searchpair() skip expr

Problem:    Syntax highlighting disabled when using synID() in searchpair()
            skip expression and it times out. (Jaehwang Jung)
Solution:   Add the redrawtime_limit_set flag. (closes #10562)
diff --git a/src/drawscreen.c b/src/drawscreen.c
index 2c184bd..4fea562 100644
--- a/src/drawscreen.c
+++ b/src/drawscreen.c
@@ -2179,6 +2179,7 @@
 #endif
 #ifdef SYN_TIME_LIMIT
     // Set the time limit to 'redrawtime'.
+    redrawtime_limit_set = TRUE;
     init_regexp_timeout(p_rdt);
 #endif
 #ifdef FEAT_FOLDING
@@ -2692,6 +2693,7 @@
 
 #ifdef SYN_TIME_LIMIT
     disable_regexp_timeout();
+    redrawtime_limit_set = FALSE;
 #endif
 
     // Reset the type of redrawing required, the window has been updated.