Fix bugs flagged in code review of jsonpull C++ port

- jsontool.cpp `out()`: route JSON_NUMBER (and anything else non-string)
  through `json_stringify` instead of `o->string()`, which now asserts
  on a non-string type and would crash `--extract` on numeric attributes.
- geojson.{hpp,cpp} `json_end_map`: take `json_pull_ptr` by reference so
  the caller's shared_ptr is released, null-guard before touching
  `jp->source`, and clear `jp->source` after delete to avoid a dangling
  pointer.
- jsonpull/jsonpull.cpp: low-surrogate range check was comparing the
  outer-loop byte `c` instead of the parsed code unit `ch`, breaking
  surrogate-pair decoding for some \\uXXXX escapes. Pre-existing bug
  preserved across the port.
- tile-join.cpp `handle_vector_layers`: require the field value to have
  type JSON_STRING (and the key to be non-null) before calling
  `string()`; the previous truthy `type` check would assert on a
  non-string value.

Co-authored-by: Cursor <cursoragent@cursor.com>

geojson.cpp

@@ -306,7 +306,11 @@ json_pull_ptr json_begin_map(char *map, long long len) {
 	return json_begin(json_map_read, jm);
 }
 
-void json_end_map(json_pull_ptr jp) {
+void json_end_map(json_pull_ptr &jp) {
+	if (jp == nullptr) {
+		return;
+	}
 	delete (struct jsonmap *) jp->source;
+	jp->source = nullptr;
 	json_end(jp);
 }

geojson.hpp

@@ -22,7 +22,7 @@ struct parse_json_args {
 };
 
 json_pull_ptr json_begin_map(char *map, long long len);
-void json_end_map(json_pull_ptr jp);
+void json_end_map(json_pull_ptr &jp);
 
 void parse_json(struct serialization_state *sst, json_pull_ptr jp, int layer, std::string layername);
 void *run_parse_json(void *v);

jsonpull/jsonpull.cpp

@@ -551,7 +551,7 @@ again:
 							surrogate = ch;
 						}
 						continue;
-					} else if (ch >= 0xdc00 && c <= 0xdfff) {
+					} else if (ch >= 0xdc00 && ch <= 0xdfff) {
 						if (surrogate >= 0) {
 							long c1 = surrogate - 0xd800;
 							long c2 = ch - 0xdc00;

jsontool.cpp

@@ -148,9 +148,13 @@ void out(std::string const &s, int type, json_object_ptr properties) {
 		json_object_ptr o = json_hash_get(properties, extract);
 		if (o != nullptr) {
 			found = true;
-			if (o->type == JSON_STRING || o->type == JSON_NUMBER) {
+			if (o->type == JSON_STRING) {
 				extracted = sort_quote(o->string().c_str());
 			} else {
+				// Numbers, booleans, null, and any other non-string
+				// values are rendered via json_stringify(); calling
+				// o->string() here would assert because the type-tagged
+				// accessor requires JSON_STRING.
 				extracted = sort_quote(json_stringify(o).c_str());
 			}
 		}

tile-join.cpp

@@ -1035,7 +1035,8 @@ void handle_vector_layers(json_object_ptr vector_layers, std::map<std::string, l
 				json_object_ptr fields = json_hash_get(vector_layers->array()[i], "fields");
 				if (fields != nullptr && fields->type == JSON_HASH) {
 					for (const auto &e : fields->entries()) {
-						if (e.key->type == JSON_STRING && e.value->type) {
+						if (e.key != nullptr && e.key->type == JSON_STRING &&
+						    e.value != nullptr && e.value->type == JSON_STRING) {
 							const std::string &desc2 = e.value->string();
 
 							if (desc2 != "Number" &&