[eria2c] Fix --skip-unavailable fragment

yt_dlp/downloader/external.py

@@ -115,7 +115,14 @@ class ExternalFD(FragmentFD):
 
         self._debug_cmd(cmd)
 
-        if 'fragments' in info_dict:
+        if 'fragments' not in info_dict:
+            p = subprocess.Popen(
+                cmd, stderr=subprocess.PIPE)
+            _, stderr = process_communicate_or_kill(p)
+            if p.returncode != 0:
+                self.to_stderr(stderr.decode('utf-8', 'replace'))
+            return p.returncode
+
         fragment_retries = self.params.get('fragment_retries', 0)
         skip_unavailable_fragments = self.params.get('skip_unavailable_fragments', True)
 
@@ -157,13 +164,7 @@ class ExternalFD(FragmentFD):
                 os.remove(encodeFilename(fragment_filename))
         dest.close()
         os.remove(encodeFilename('%s.frag.urls' % tmpfilename))
-        else:
+        return 0
-            p = subprocess.Popen(
-                cmd, stderr=subprocess.PIPE)
-            _, stderr = process_communicate_or_kill(p)
-            if p.returncode != 0:
-                self.to_stderr(stderr.decode('utf-8', 'replace'))
-        return p.returncode
 
 
 class CurlFD(ExternalFD):