Avoid (possible) undefined behaviour in hc_fclose(), and don't assume plain file

src/filehandling.c

@@ -596,7 +596,7 @@ void hc_fclose (HCFILE *fp)
 
     unzClose (fp->ufp);
   }
-  else
+  else if (fp->pfp)
   {
     fclose (fp->pfp);
   }

src/potfile.c

@@ -211,8 +211,6 @@ void potfile_read_close (hashcat_ctx_t *hashcat_ctx)
 
   if (hashconfig->potfile_disable == true) return;
 
-  if (potfile_ctx->fp.pfp == NULL) return;
-
   hc_fclose (&potfile_ctx->fp);
 }