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 stleary#758.

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

@@ -253,7 +253,11 @@ public JSONObject(JSONTokener x) throws JSONException {
             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();

src/test/java/org/json/junit/JSONObjectTest.java

@@ -2225,6 +2225,15 @@ public void jsonObjectParsingErrors() {
                     "Expected a ',' or '}' at 15 [character 16 line 1]",
                     e.getMessage());
         }
+        try {
+            // \0 after ,
+            String str = "{\"myKey\":true, \0\"myOtherKey\":false}";
+            assertNull("Expected an exception",new JSONObject(str));
+        } catch (JSONException e) {
+          assertEquals("Expecting an exception message",
+              "A JSONObject text must end with '}' at 15 [character 16 line 1]",
+              e.getMessage());
+        }
         try {
             // append to wrong key
             String str = "{\"myKey\":true, \"myOtherKey\":false}";