[fix] SQLiteIndex: Do not fall back to libarchive when the specified …

…index cannot be read or written

core/ratarmountcore/SQLiteIndex.py

@@ -250,17 +250,26 @@ def getPossibleIndexFilePaths(
         archiveFilePath: Optional[str] = None,
         ignoreCurrentFolder: bool = False,
     ) -> List[str]:
+        if indexFilePath == ':memory:':
+            return []
+
+        # Prior versions did simply return indexFilePath as the only possible path if it was specified.
+        # This worked well enough because if the path did not exist, it would simply be created.
+        # However, for non-writable locations, or if parent folders are missing, or for remote URLs,
+        # this will fail badly and result in TAR files being opened with the fallback, libarchive, instead,
+        # which is unwanted behavior. It should fall back to another index storage location instead.
+        possibleIndexFilePaths = []
         if indexFilePath:
-            return [] if indexFilePath == ':memory:' else [os.path.abspath(os.path.expanduser(indexFilePath))]
+            possibleIndexFilePaths.append(os.path.abspath(os.path.expanduser(indexFilePath)))
 
         if not archiveFilePath:
-            return []
+            return possibleIndexFilePaths
 
         defaultIndexFilePath = archiveFilePath + ".index.sqlite"
         if not indexFolders:
-            return [defaultIndexFilePath, ':memory:']
+            possibleIndexFilePaths.extend([defaultIndexFilePath, ':memory:'])
+            return possibleIndexFilePaths
 
-        possibleIndexFilePaths = []
         indexPathAsName = defaultIndexFilePath.replace("/", "_")
         for folder in indexFolders:
             if folder: