SSL: fix overflow error.
SSL: fix overflow error.

In the previous code, the addition was performed as an unsigned char. This
means that a value of 255 would wrap to 0 and throw us into a loop.

BUG=none
TEST=Have the server send an NPN extension with an element of length 255.

http://codereview.chromium.org/500032

git-svn-id: dd90618784b6a4b323ea0c23a071cb1c9e6f2ac7@34621 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser