patch 8.2.0832: compiler warning for uninitialized variable

Problem:    Compiler warning for uninitialized variable. (Tony Mechelynck)
Solution:   Add initial value.
diff --git a/src/map.c b/src/map.c
index 6c92633..4f0c870 100644
--- a/src/map.c
+++ b/src/map.c
@@ -2187,7 +2187,7 @@
     int		abbr = FALSE;
     int		get_dict = FALSE;
     mapblock_T	*mp;
-    mapblock_T	*mp_simplified;
+    mapblock_T	*mp_simplified = NULL;
     int		buffer_local;
     int		flags = REPTERM_FROM_PART | REPTERM_DO_LT;