win32: fix bb_get_last_path_component_nostrip()

Finding the last component of a path didn't properly handle a
mixture of slashes and backslashes, paths relative to another
drive or bare UNC paths.  The following were incorrect:

   $ basename /dir\\file
   dir\file
   $ basename c:file
   c:file
   $ basename //HOST/share
   share

With this patch the results are now:

   $ basename /dir\\file
   file
   $ basename c:file
   file
   $ basename //HOST/share
   //HOST/share

1 files changed, 11 insertions, 5 deletions

diff --git a/libbb/get_last_path_component.c b/libbb/get_last_path_component.c
index 00649620d..06033e139 100644
--- a/libbb/get_last_path_component.c
+++ b/libbb/get_last_path_component.c
@@ -31,17 +31,23 @@ const char* FAST_FUNC bb_basename(const char *name)
  */
 char* FAST_FUNC bb_get_last_path_component_nostrip(const char *path)
 {
-        char *slash = strrchr(path, '/');
-
 #if ENABLE_PLATFORM_MINGW32
-        const char *start = has_dos_drive_prefix(path) ? path+2 : path;
+        const char *start = path + root_len(path);
+        char *slash = strrchr(start, '/');
+        char *bslash = strrchr(start, '\\');
 
-        if (!slash)
-                slash = strrchr(path, '\\');
+        if (slash && bslash)
+                slash = MAX(slash, bslash);
+        else if (!slash)
+                slash = bslash;
 
+        if (!slash && has_dos_drive_prefix(path) && path[2] != '\0')
+                return (char *)path + 2;
         if (!slash || (slash == start && !slash[1]))
                 return (char*)path;
 #else
+        char *slash = strrchr(path, '/');
+
         if (!slash || (slash == path && !slash[1]))
                 return (char*)path;
 #endif