Fix lfc_ensure_function which now disables LFC (#5294)

## Problem

There was a bug in lfc_ensure_opened which actually disables LFC

## Summary of changes

Return true ifLFC file is normally opened

## Checklist before requesting a review

- [ ] I have performed a self-review of my code.
- [ ] If it is a core feature, I have added thorough tests.
- [ ] Do we need to implement analytics? if so did you add the relevant
metrics to the dashboard?
- [ ] If this PR requires public announcement, mark it with
/release-notes label and add several sentences in this section.

## Checklist before merging

- [ ] Do not forget to reformat commit message to not include the above
checklist

Co-authored-by: Konstantin Knizhnik <knizhnik@neon.tech>

pgxn/neon/file_cache.c

@@ -153,7 +153,7 @@ lfc_ensure_opened(void)
 			return false;
 		}
 	}
-	return false;
+	return true;
 }
 
 static void
@@ -640,6 +640,7 @@ lfc_write(NRelFileInfo rinfo, ForkNumber forkNum, BlockNumber blkno,
 	rc = pwrite(lfc_desc, buffer, BLCKSZ, ((off_t)entry->offset*BLOCKS_PER_CHUNK + chunk_offs)*BLCKSZ);
 	if (rc != BLCKSZ)
 	{
+		LWLockRelease(lfc_lock);
 		lfc_disable("write");
 	}
 	else
@@ -650,9 +651,8 @@ lfc_write(NRelFileInfo rinfo, ForkNumber forkNum, BlockNumber blkno,
 			dlist_push_tail(&lfc_ctl->lru, &entry->lru_node);
 
 		entry->bitmap[chunk_offs >> 5] |= (1 << (chunk_offs & 31));
+		LWLockRelease(lfc_lock);
 	}
-
-	LWLockRelease(lfc_lock);
 }
 
 /*