Don't skip past \0 when parsing JSON objects.

A better solution might be to use -1 instead 0 to represent EOF everywhere,
which of course means changing `char` variables to `int`. The solution here is
enough to solve the immediate problem, though.

Fixes #758.

src/main/java/org/json/JSONObject.java

@@ -253,7 +253,11 @@ public class JSONObject {
             switch (x.nextClean()) {
             case ';':
             case ',':
-                if (x.nextClean() == '}') {
+                c = x.nextClean();
+                if (c == 0) {
+                    throw x.syntaxError("A JSONObject text must end with '}'");
+                }
+                if (c == '}') {
                     return;
                 }
                 x.back();