patch 9.1.0959: Coverity complains about type conversion

Problem:  Coverity complains about type conversion
          (after v9.1.0957)
Solution: use size_t instead of int for file length
          (Yegappan Lakshmanan)

closes: #16297

Signed-off-by: Yegappan Lakshmanan <yegappan@yahoo.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/ex_docmd.c b/src/ex_docmd.c
index d516755..4438834 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -9700,7 +9700,7 @@
     char_u	*s;
     char_u	*result;
     char_u	*resultbuf = NULL;
-    int		resultlen;
+    size_t	resultlen;
     buf_T	*buf;
     int		valid = VALID_HEAD + VALID_PATH;    // assume valid result
     int		spec_idx;
@@ -9975,12 +9975,12 @@
 		break;
 	}
 
-	resultlen = (int)STRLEN(result);	// length of new string
+	resultlen = STRLEN(result);	// length of new string
 	if (src[*usedlen] == '<')	// remove the file name extension
 	{
 	    ++*usedlen;
 	    if ((s = vim_strrchr(result, '.')) != NULL && s >= gettail(result))
-		resultlen = (int)(s - result);
+		resultlen = s - result;
 	}
 	else if (!skip_mod)
 	{