Text search: normalize input text

So that Unicode NFC normalization can combine diacritics
entered via our keyboard with their base into their
canonical form (we can expect books text to be normalized).

frontend/apps/reader/modules/readersearch.lua

@@ -6,6 +6,7 @@ local InfoMessage = require("ui/widget/infomessage")
 local InputDialog = require("ui/widget/inputdialog")
 local Notification = require("ui/widget/notification")
 local UIManager = require("ui/uimanager")
+local Utf8Proc = require("ffi/utf8proc")
 local WidgetContainer = require("ui/widget/container/widgetcontainer")
 local logger = require("logger")
 local _ = require("gettext")
@@ -83,7 +84,11 @@ end
 function ReaderSearch:searchCallback(reverse)
     local search_text = self.input_dialog:getInputText()
     if search_text == "" then return end
-    self.last_search_text = search_text
+    -- search_text comes from our keyboard, and may contain multiple diacritics ordered
+    -- in any order: we'd rather have them normalized, and expect the book content to
+    -- be proper and normalized text.
+    self.last_search_text = search_text -- if shown again, show it as it has been inputted
+    search_text = Utf8Proc.normalize_NFC(search_text)
     self.use_regex = self.check_button_regex.checked
     self.case_insensitive = not self.check_button_case.checked
     local regex_error = self.use_regex and self.ui.document:checkRegex(search_text)