fix: force disk fallback in LocatorConverter to fix MD/TXT reading position (#40)

Background pre-processing for single-file imports (MD/TXT) was generating empty DB cache entries because it only looked at RAM content. This caused position saves in Vertical Mode to fail. This fix ensures that an empty cache entry triggers a disk-read fallback to generate valid semantic blocks on-demand.

app/src/main/java/com/aryan/reader/pdf/PdfViewerScreen.kt

@@ -1677,6 +1677,7 @@ fun PdfViewerScreen(
             )
 
             if (result == SnackbarResult.ActionPerformed) {
+                snackbarHostState.currentSnackbarData?.dismiss()
                 val item = uiState.recentFiles.find { it.bookId == reflowBookId }
                 if (item != null) {
                     viewModel.onRecentFileClicked(item)