Fix variable scope

execute.py

@@ -172,7 +172,7 @@ def unsafe_execute_java(check_program, result, timeout):
         open(f"Main.java", 'w').write(check_program)
 
         res = "failed: unknown error"
-        compile_returncode = -1
+        compile_returncode, compilation_result = -1, None
         for _ in range(5):
             try:
                 compilation_result = subprocess.run(
@@ -183,7 +183,9 @@ def unsafe_execute_java(check_program, result, timeout):
             except subprocess.TimeoutExpired as e:
                 continue
         if compile_returncode != 0:
-            err = compilation_result.stderr.decode() if compilation_result.stderr else compilation_result.stdout.decode()
+            err = "unknown error"
+            if compilation_result is not None:
+                err = compilation_result.stderr.decode() if compilation_result.stderr else compilation_result.stdout.decode()
             res = "failed: compilation error: " + err
         else:
             try: