only append .exe suffix on Windows if the executable is called with t…

…he full path

pre_commit/languages/r.py

@@ -62,11 +62,10 @@ def _prefix_if_non_local_file_entry(
 
 def _rscript_exec() -> str:
     r_home = os.environ.get('R_HOME')
-    program = win_exe(RSCRIPT_PROGRAM)
     if r_home is None:
-        return program
+        return RSCRIPT_PROGRAM
     else:
-        return os.path.join(r_home, 'bin', program)
+        return os.path.join(r_home, 'bin', win_exe(RSCRIPT_PROGRAM))
 
 
 def _entry_validate(entry: Sequence[str]) -> None: