break out fs_isdir and use it to test fs argument

src/studio/fs.c

@@ -545,6 +545,15 @@ static void onEnumPublicDirsDone(void* data)
     free(enumPublicDirsData);
 }
 
+bool fs_isdir(const char* path)
+{
+    struct tic_stat_struct s;
+    const FsString* pathString = utf8ToString(path);
+    bool isdir = tic_stat(pathString, &s) == 0 && S_ISDIR(s.st_mode);
+    freeString(pathString);
+    return isdir;
+}
+
 bool tic_fs_isdir(tic_fs* fs, const char* name)
 {
     if (*name == '.') return false;
@@ -559,13 +568,7 @@ bool tic_fs_isdir(tic_fs* fs, const char* name)
 
     return s.fattrib & AM_DIR;
 #else
-    const char* path = tic_fs_path(fs, name);
-    struct tic_stat_struct s;
-    const FsString* pathString = utf8ToString(path);
-    bool ret = tic_stat(pathString, &s) == 0 && S_ISDIR(s.st_mode);
-    freeString(pathString);
-
-    return ret;
+    return fs_isdir(tic_fs_path(fs, name));
 #endif
 }
 

src/studio/fs.h

@@ -59,6 +59,7 @@ void    tic_fs_homedir      (tic_fs* fs);
 
 u64     fs_date     (const char* name);
 bool    fs_exists   (const char* name);
+bool    fs_isdir    (const char* path);
 void*   fs_read     (const char* path, s32* size);
 bool    fs_write    (const char* path, const void* data, s32 size);
 void    fs_enum     (const char* path, fs_list_callback callback, void* data);

src/studio/studio.c

@@ -2749,7 +2749,7 @@ Studio* studio_create(s32 argc, char **argv, s32 samplerate, tic80_pixel_color_f
     {
         const char *path = args.fs ? args.fs : folder;
 
-        if (fs_exists(path))
+        if (fs_isdir(path))
         {
             studio->fs = tic_fs_create(path,
 #if defined(BUILD_EDITORS)
@@ -2761,7 +2761,7 @@ Studio* studio_create(s32 argc, char **argv, s32 samplerate, tic80_pixel_color_f
         }
         else
         {
-            fprintf(stderr, "error: folder `%s` doesn't exist\n", path);
+            fprintf(stderr, "error: `%s` is not a folder\n", path);
             exit(1);
         }
     }