Fix pattern matching for 'signed' tolower() platforms, noted by rpluem

git-svn-id: https://svn.apache.org/repos/asf/apr/apr-util/branches/0.9.x@781066 13f79535-47bb-0310-9956-ffa450edef68

strmatch/apr_strmatch.c

@@ -74,7 +74,7 @@ static const char *match_boyer_moore_horspool_nocase(
             }
             s_tmp--;
         }
-        s_next += shift[apr_tolower(*s_next)];
+        s_next += shift[(unsigned char)apr_tolower(*s_next)];
     }
     return NULL;
 }