When serializing with JSON_C_TO_STRING_PRETTY set, keep the opening and closing curly or square braces on same line for empty objects or arrays. Issue #778.

tests/test1Formatted_plain.expected

@@ -75,4 +75,4 @@ my_object=
 	foo: "bar"
 	bool0: false
 	bool1: true
-my_object.to_string()={"abc":12,"foo":"bar","bool0":false,"bool1":true}
+my_object.to_string()={"abc":12,"foo":"bar","bool0":false,"bool1":true,"empty_array":[],"empty_obj":{}}