Fix trailing whitespace when dumping dicts with indent

When dumping a dict with indent > 0, `dict_to_json` would insert extra trailing whitespace before the opening and closing newlines of the dict.
Also, when dumping an empty dict, two newlines would be inserted.

This commit fixes both of these issues.

Author: laomaiweng

json5/dumper.py

@@ -89,8 +89,9 @@ def dump(self, obj: Any) -> Any:
     def dict_to_json(self, d: dict[Any, Any]) -> Any:
         self.env.write('{', indent=0)
         if self.env.indent:
-            self.env.write('\n')
+            self.env.write('\n', indent=0)
             self.env.indent_level += 1
+        index = 0
         for index, (key, value) in enumerate(d.items(), start=1):
             if self.env.indent:
                 self.env.write('')
@@ -107,7 +108,8 @@ def dict_to_json(self, d: dict[Any, Any]) -> Any:
 
         if self.env.indent:
             self.env.indent_level -= 1
-            self.env.write('\n')
+            if index != 0:
+                self.env.write('\n', indent=0)
             self.env.write('}')
         else:
             self.env.write('}', indent=0)