patch 8.2.5125: MS-Windows: warnings from MinGW compiler

Problem:    MS-Windows: warnings from MinGW compyler.
Solution:   Use "volatile". (Yasuhiro Matsumoto, closes #10589)  Initialize
            variable.
diff --git a/src/map.c b/src/map.c
index 9570285..2850a3f 100644
--- a/src/map.c
+++ b/src/map.c
@@ -1273,7 +1273,7 @@
     int		i;
     int		fuzzy;
     int		match;
-    int		score;
+    int		score = 0;
     fuzmatch_str_T  *fuzmatch;
 
     fuzzy = cmdline_fuzzy_complete(pat);