Start work on fixing #1173 issues

Author: cowtowncoder

src/main/java/com/fasterxml/jackson/core/json/ReaderBasedJsonParser.java

@@ -2387,6 +2387,7 @@ private final int _skipColon2(boolean gotColon) throws IOException
                     return i;
                 }
                 if (i != INT_COLON) {
+                    --_inputPtr; // for correct error reporting
                     _reportUnexpectedChar(i, "was expecting a colon to separate field name and value");
                 }
                 gotColon = true;