Fixed bug in find function causing crash

Emptying the search field of the find function caused the program to
crash.

Signed-off-by: Malte Splietker <malte.splietker@gmail.com>

src/gui/SearchBar.cpp

@@ -84,7 +84,7 @@ void SearchBar::search(const char* text)
 	}
 	else
 	{
-		searchTextonCurrentPage(NULL, NULL, NULL);
+		searchTextonCurrentPage("", NULL, NULL);
 		gtk_label_set_text(GTK_LABEL(lbSearchState), "");
 	}