Move LocaleScanner's INHERIT check from find upstream to __find

When digesting CLDR v44.1's github form, some data (e.g. pt_BR's
language endonym) were None that had perfectly sensible values in the
zip-file form.  Letting __find() yield INHERIT entries lead to find()
sometimes returning None, where __find() should have tried harder or
raised an Error.

This further amends commit bcdd51cfae24731a73d008add23d3c1e85bbd8d0
(after commit 0f770b0b34bcb5fa0a598b2ff76fe215fbc25f5c isolated its
magic value).

Pick-to: 6.5
Task-number: QTBUG-115158
Change-Id: I1af92a687cd50b8fd026c25f068c804a3516ef95
Reviewed-by: Mate Barany <mate.barany@qt.io>
(cherry picked from commit 43cb4136a92331d1137ddd7453e7bb4ca130ecff)
Reviewed-by: Cristian Maureira-Fredes <cristian.maureira-fredes@qt.io>

util/locale_database/ldml.py

@@ -207,9 +207,7 @@ class LocaleScanner (object):
             for elt in self.__find(xpath):
                 try:
                     if draft is None or elt.draft <= draft:
-                        value = elt.dom.firstChild.nodeValue
-                        if value != INHERIT:
-                            return value
+                        return elt.dom.firstChild.nodeValue
                 except (AttributeError, KeyError):
                     pass
         except Error as e:
@@ -420,6 +418,7 @@ class LocaleScanner (object):
                     break
 
             else: # Found matching elements
+                elts = tuple(self.__skipInheritors(elts))
                 if elts:
                     foundNone = False
                 # Possibly filter elts to prefer the least drafty ?
@@ -448,6 +447,7 @@ class LocaleScanner (object):
                         raise Error(f'All lack child {selector} for {sought} in {self.name}')
 
             else: # Found matching elements
+                roots = tuple(self.__skipInheritors(roots))
                 if roots:
                     foundNone = False
                 for elt in roots:
@@ -459,6 +459,15 @@ class LocaleScanner (object):
                 sought += f' (for {xpath})'
             raise Error(f'No {sought} in {self.name}')
 
+    @staticmethod
+    def __skipInheritors(elts):
+        for elt in elts:
+            try:
+                if elt.dom.firstChild.nodeValue != INHERIT:
+                    yield elt
+            except (AttributeError, KeyError):
+                yield elt
+
     def __currencyDisplayName(self, stem):
         try:
             return self.find(stem + 'displayName')