Fix issue #1702 (crash without internet) (#1703)

* Fix issue #1702 (crash without internet)

* Use ConnectionError

Co-authored-by: norhh <nikhilparasaram@gmail.com>

mythril/ethereum/util.py

@@ -10,6 +10,7 @@ import solc
 import re
 
 from pathlib import Path
+from requests.exceptions import ConnectionError
 from subprocess import PIPE, Popen
 from typing import Optional
 
@@ -139,7 +140,11 @@ def solc_exists(version):
     return solc_binary
 
 
-all_versions = solcx.get_installable_solc_versions()
+try:
+    all_versions = solcx.get_installable_solc_versions()
+except ConnectionError:
+    # No internet, trying to proceed with installed compilers
+    all_versions = solcx.get_installed_solc_versions()
 
 
 def extract_version(file: str) -> Optional[str]: