bug #12620 (UTF-8 indexing causes ER_NO_KEYFILE error)

The problem is that on some Mac OS X-es the file writing/reading
call with zero bytes to read/write returns error.
So here i try to eliminate that kinds of calls.

myisam/mi_check.c

@@ -1366,7 +1366,8 @@ int mi_repair(MI_CHECK *param, register MI_INFO *info,
 			   param->temp_filename);
       goto err;
     }
-    if (filecopy(param,new_file,info->dfile,0L,new_header_length,
+    if (new_header_length &&
+        filecopy(param,new_file,info->dfile,0L,new_header_length,
 		 "datafile-header"))
       goto err;
     info->s->state.dellink= HA_OFFSET_ERROR;
@@ -2063,7 +2064,8 @@ int mi_repair_by_sort(MI_CHECK *param, register MI_INFO *info,
 			   param->temp_filename);
       goto err;
     }
-    if (filecopy(param, new_file,info->dfile,0L,new_header_length,
+    if (new_header_length &&
+        filecopy(param, new_file,info->dfile,0L,new_header_length,
 		 "datafile-header"))
       goto err;
     if (param->testflag & T_UNPACK)
@@ -2431,7 +2433,8 @@ int mi_repair_parallel(MI_CHECK *param, register MI_INFO *info,
 			   param->temp_filename);
       goto err;
     }
-    if (filecopy(param, new_file,info->dfile,0L,new_header_length,
+    if (new_header_length &&
+        filecopy(param, new_file,info->dfile,0L,new_header_length,
 		 "datafile-header"))
       goto err;
     if (param->testflag & T_UNPACK)

mysys/my_chsize.c

@@ -44,7 +44,9 @@ int my_chsize(File fd, my_off_t newlength, int filler, myf MyFlags)
   DBUG_PRINT("my",("fd: %d  length: %lu  MyFlags: %d",fd,(ulong) newlength,
 		   MyFlags));
 
-  oldsize = my_seek(fd, 0L, MY_SEEK_END, MYF(MY_WME+MY_FAE));
+  if ((oldsize = my_seek(fd, 0L, MY_SEEK_END, MYF(MY_WME+MY_FAE))) == newlength)
+    DBUG_RETURN(0);
+
   DBUG_PRINT("info",("old_size: %ld", (ulong) oldsize));
 
   if (oldsize > newlength)