Patch for Bug 163098

[Frank Reininghaus]

Hi everyone,

I've looked a bit into
http://bugs.kde.org/show_bug.cgi?id=163098
(crashes Konqueror and Dolphin if you enable "Automatic" text completion in 
the location bar, enter any 1-character string that prompts a completion and 
hit backspace).

The problem seems to be in the method KUrlCompletionPrivate::MyURL::init in 
the file kdelibs/kio/kio/kurlcompletion.cpp. The method at() of the QString 
url_copy is called a few times to get the first character of url_copy without 
checking if the string url_copy is empty.

When reproducing this bug, url_copy is indeed empty after hitting backspace,
and this causes the crash. I'm attaching a patch that fixes the problem for me 
in trunk (note that my patch in comment 9 of the bug report only fixes part 
of it). This just replaces 

url_copy.at(0) == QLatin1Char('$') ||
url_copy.at(0) == QLatin1Char('~') )

by

!url_copy.isEmpty () && 
	( url_copy.at(0) == QLatin1Char('$') ||
	url_copy.at(0) == QLatin1Char('~') ))

to make sure that the string is not empty before its first character is 
examined.

It's just a suggestion - maybe someone who is more familiar with the code can 
come up with a better idea...

Cheers
Frank
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