properly check for basepacks

src/pc/fs/fs.c

@@ -43,8 +43,8 @@ static inline fs_dir_t *fs_find_dir(const char *realpath) {
 }
 
 static int mount_cmp(const void *p1, const void *p2) {
-    const char *s1 = *(const char **)p1;
-    const char *s2 = *(const char **)p2;
+    const char *s1 = sys_file_name(*(const char **)p1);
+    const char *s2 = sys_file_name(*(const char **)p2);
 
     // check if one or both of these are basepacks
     const int plen = strlen(FS_BASEPACK_PREFIX);

src/pc/platform.c

@@ -49,15 +49,22 @@ int sys_strcasecmp(const char *s1, const char *s2) {
     return result;
 }
 
-const char *sys_file_extension(const char *fname) {
+const char *sys_file_extension(const char *fpath) {
+    const char *fname = sys_file_name(fpath);
     const char *dot = strrchr(fname, '.');
-    const char *sep = strrchr(fname, '/');
-    if (!sep) sep = strrchr(fname, '\\');
     if (!dot || !dot[1]) return NULL; // no dot
-    if (dot <= sep + 1) return NULL; // dot is before the last separator or right after it (e.g. /.local)
+    if (dot == fname) return NULL; // dot is the first char (e.g. .local)
     return dot + 1;
 }
 
+const char *sys_file_name(const char *fpath) {
+    const char *sep1 = strrchr(fpath, '/');
+    const char *sep2 = strrchr(fpath, '\\');
+    const char *sep = sep1 > sep2 ? sep1 : sep2;
+    if (!sep) return fpath;
+    return sep + 1;
+}
+
 /* this calls a platform-specific impl function after forming the error message */
 
 static void sys_fatal_impl(const char *msg) __attribute__ ((noreturn));

src/pc/platform.h

@@ -20,7 +20,8 @@ int sys_strcasecmp(const char *s1, const char *s2);
 // path stuff
 const char *sys_user_path(void);
 const char *sys_exe_path(void);
-const char *sys_file_extension(const char *fname);
+const char *sys_file_extension(const char *fpath);
+const char *sys_file_name(const char *fpath);
 
 // shows an error message in some way and terminates the game
 void sys_fatal(const char *fmt, ...) __attribute__ ((noreturn));