Only clear search with :search if one is displayed

For some reason, calling search.clear() while no search is displayed causes the
backends to un-focus inputs, and with QtWebKit, even hinting can't focus them
again after that.

CHANGELOG.asciidoc

@@ -49,6 +49,8 @@ Changed
 - Using `:download` now uses the page's title as filename.
 - Using `:back` or `:forward` with a count now skips intermediate pages.
 - When there are multiple messages shown, the timeout is increased.
+- `:search` now only clears the search if one was displayed before, so pressing
+  `<Escape>` doesn't un-focus inputs anymore.
 
 Fixes
 ~~~~~

qutebrowser/browser/commands.py

@@ -1744,7 +1744,8 @@ class CommandDispatcher:
         """
         self.set_mark("'")
         tab = self._current_widget()
-        tab.search.clear()
+        if tab.search.search_displayed:
+            tab.search.clear()
 
         if not text:
             return