Fix object stream parsing

Commit 8cc27b6 broke object stream parsing by resetting the content
cursor PDFParser.charCounter to zero on every invocation. This broke object
stream parsing. Reproducer:

$ echo -e "create pdf\ncreate object_stream\nall\nsave /tmp/foo.pdf" | \
	peepdf -i

Without fix:

$ peepdf -j /tmp/foo.pdf
Error: An error has occurred while parsing an indirect object!!

With this change: JSON output as expected (same for other outputs).

$ peepdf -j /tmp/foo.pdf
{
    "peepdf_analysis": {
[...]
           "version": "0.3"
        }
    }
}

peepdf/PDFCore.py

@@ -8153,7 +8153,6 @@ def readUntilSymbol(self, string, symbol):
 
         newString = string[self.charCounter:]
 
-        self.charCounter = 0
         index = newString.find(symbol)
         if index == -1:
             errorMessage = 'Symbol "'+symbol+'" not found'