fix: Guard against uninitialized hashmap in key removal

Removing non-present keys is a supported operation on HashMaps,
and most other operations are well-defined on uninitialized
HashMaps.

Currently, removing any key on an uninitialized HashMap will
result in an 'Array index out of bounds' error.

This change guards against such a case.

lib/std/collections/map.c3

@@ -369,6 +369,7 @@ fn void HashMap.free_internal(&map, void* ptr) @inline @private
 
 fn bool HashMap.remove_entry_for_key(&map, Key key) @private
 {
+	if (!map.count) return false;
 	uint hash = rehash(key.hash());
 	uint i = index_for(hash, map.table.len);
 	Entry* prev = map.table[i];
@@ -421,4 +422,4 @@ struct Entry
 	Key key;
 	Value value;
 	Entry* next;
-}
+}