App.get_value(): Fix FileNotFoundError regression

The refactored __get_project_conf() raises FileNotFoundError when project.conf does not exist, whereas the original read_value() returns None. This causes get_value() to crash for projects with missing or incomplete project.conf files.
Catch FileNotFoundError in __get_project_conf() and return None to restore original behavior. Remove redundant @cache from __read_project_conf() since __get_project_conf() already provides caching.
Assisted-by: unsloth/Qwen3.6-35B-A3B-GGUF:IQ4_NL and pi.dev
Signed-off-by: Jan Lindemann <jan@janware.com>

src/python/jw/pkg/App.py

@@ -185,16 +185,18 @@ class App(Base):
                 return ret
         return None
 
-    @cache
     def __read_project_conf(self, project_dir: str) -> ProjectConf:
         return ProjectConf.read(project_dir + '/make/project.conf')
 
     @cache
-    def __get_project_conf(self, project: str) -> ProjectConf:
+    def __get_project_conf(self, project: str) -> ProjectConf | None:
         pd = self.__proj_dir(project, False)
         if pd is None:
             raise Exception(f'Failed to find directory of project {project}')
-        return self.__read_project_conf(pd)
+        try:
+            return self.__read_project_conf(pd)
+        except FileNotFoundError:
+            return None
 
     def __get_project_refs_cached(
         self, buf, visited, spec, section, key, add_self, scope, names_only
@@ -552,7 +554,10 @@ class App(Base):
                     log(DEBUG, f'Ignoring unreadable file "{version_path}"')
                     continue
             raise Exception(f'No version file found for project "{project}"')
-        ret = self.__get_project_conf(project).get_str_or_none(section, key)
+        proj_conf = self.__get_project_conf(project)
+        if proj_conf is None:
+            return None
+        ret = proj_conf.get_str_or_none(section, key)
         log(
             DEBUG,
             'Lookup %s -> %s / [%s%s] -> "%s"' %