Fix compilation error for redefinition of jsonIsspace (#75)

* Fix compilation error for redefinition of jsonIsspace when including in amalgamation build of sqlite3.c

* Fix redefinition variable jsonIsSpaceX[]

* Add check for SQLITE_AMALGMATION

* Add check for SQLITE_CORE

sqlite-vec.c

@@ -546,6 +546,7 @@ static f32 distance_hamming(const void *a, const void *b, const void *d) {
   return distance_hamming_u8((u8 *)a, (u8 *)b, dimensions / CHAR_BIT);
 }
 
+#if !defined(SQLITE_CORE) || (defined(SQLITE_AMALGAMATION) && defined(SQLITE_OMIT_JSON))
 // from SQLite source:
 // https://github.com/sqlite/sqlite/blob/a509a90958ddb234d1785ed7801880ccb18b497e/src/json.c#L153
 static const char jsonIsSpaceX[] = {
@@ -563,7 +564,9 @@ static const char jsonIsSpaceX[] = {
     0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
     0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 };
+
 #define jsonIsspace(x) (jsonIsSpaceX[(unsigned char)x])
+#endif
 
 typedef void (*vector_cleanup)(void *p);