nostrdb: Fix heap buffer overflow

The Address Sanitizer detected a heap buffer overflow during a memcpy operation
in nostrdb.c associated with note parsing.

It was found that not enough memory was being allocated to the buffer to
support all the content parsing.

Allocation size was increased to support the memory needed for the
parsing operations. However, the new number was not carefully calculated
as we will not run into this code path once we switch to the local relay
model.

Changelog-Fixed: Fixed memory error in nostrdb
Signed-off-by: Daniel D’Aquino <daniel@daquino.me>

nostrdb/src/nostrdb.c

@@ -7089,7 +7089,7 @@ static struct ndb_blocks *ndb_note_to_blocks(struct ndb_note *note)
 	if (content_len >= INT32_MAX)
 		return NULL;
 
-	unsigned char *buffer = malloc(content_len);
+    unsigned char *buffer = malloc(2<<18);  // Not carefully calculated, but ok because we will not need this once we switch to the local relay model
 	if (!buffer)
 		return NULL;