Add support for LFN encoding in SFN entries on WinNT

New Windows does not create LFN entries if name fits in 8.3 format and
letters in both basename and ext parts are all uppercase or all lowercase.
This commit fixes handling of lowercase letters.

src/dir_entry.rs

@@ -105,6 +105,21 @@ impl DirFileEntryData {
         &self.name
     }
 
+    pub(crate) fn lowercase_name(&self) -> String {
+        let mut name_copy: [u8; 11] = self.name;
+        if self.lowercase_basename() {
+            for c in &mut name_copy[..8] {
+                *c = (*c as char).to_ascii_lowercase() as u8;
+            }
+        }
+        if self.lowercase_ext() {
+            for c in &mut name_copy[8..] {
+                *c = (*c as char).to_ascii_lowercase() as u8;
+            }
+        }
+        ShortName::new(&name_copy).to_str().to_string()
+    }
+
     pub(crate) fn first_cluster(&self, fat_type: FatType) -> Option<u32> {
         let first_cluster_hi = if fat_type == FatType::Fat32 { self.first_cluster_hi } else { 0 };
         let n = ((first_cluster_hi as u32) << 16) | self.first_cluster_lo as u32;
@@ -139,6 +154,14 @@ impl DirFileEntryData {
         !self.is_dir()
     }
 
+    pub(crate) fn lowercase_basename(&self) -> bool {
+        self.reserved_0 & (1 << 3) != 0
+    }
+
+    pub(crate) fn lowercase_ext(&self) -> bool {
+        self.reserved_0 & (1 << 4) != 0
+    }
+
     fn created(&self) -> DateTime {
         DateTime::from_u16(self.create_date, self.create_time_1)
     }
@@ -605,7 +628,7 @@ impl <'a, 'b> DirEntry<'a, 'b> {
         if self.lfn.len() > 0 {
             String::from_utf16_lossy(&self.lfn)
         } else {
-            self.short_file_name()
+            self.data.lowercase_name()
         }
     }
     #[cfg(not(feature = "alloc"))]