Add error handling for badly formatted env vars

When no `=` is present in a line (including blank lines, which shouldn't
cause issues), the parser fails to split on `=` and throws an error.
This simply adds a try-catch around that to ignore values that would
fail.

This is a stopgap fix for #99.

web/web/models/attack.py

@@ -38,8 +38,11 @@ def envs(self) -> str:
         with open(f'/cctf/attacks/{self.id}/env') as f:
             envs = {}
             for line in f.readlines():
-                name, value = line.split('=', 1)
-                envs[name] = value
+                try:
+                    name, value = line.split('=', 1)
+                    envs[name] = value
+                except:
+                    pass
             return envs
 
     @property