[rekonq] Crash when the default search engine is not set in konqueror

[Emmanuel Surleau]

Dear all,

Rekonq's urlbar assumes rather optimistically that konqueror has a default 
search engine set. Sadly, this is not always the case, in which case reading 
from konqueror's configuration file results in an empty string. As 
"searchproviders/.desktop" does not exist, I'll let you imagine what happens 
next :(

Cheers,

Emm