patch 9.0.0119: tiny chance that creating a backup file fails

Problem:    Tiny chance that creating a backup file fails.
Solution:   Check for EEXIST error. (Ken Takata, closes #10821)

src/bufwrite.c

@@ -1208,14 +1208,22 @@ buf_write(
 		// First find a file name that doesn't exist yet (use some
 		// arbitrary numbers).
 		STRCPY(IObuff, fname);
+		fd = -1;
 		for (i = 4913; ; i += 123)
 		{
 		    sprintf((char *)gettail(IObuff), "%d", i);
 		    if (mch_lstat((char *)IObuff, &st) < 0)
-			break;
-		}
-		fd = mch_open((char *)IObuff,
+		    {
+			fd = mch_open((char *)IObuff,
 				    O_CREAT|O_WRONLY|O_EXCL|O_NOFOLLOW, perm);
+			if (fd < 0 && errno == EEXIST)
+			    // If the same file name is created by another
+			    // process between lstat() and open(), find another
+			    // name.
+			    continue;
+			break;
+		    }
+		}
 		if (fd < 0)	// can't write in directory
 		    backup_copy = TRUE;
 		else

src/version.c

@@ -735,6 +735,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    119,
 /**/
     118,
 /**/