fix 'this message is not encrypted' error in verified groups

src/dc_receive_imf.rs

@@ -1746,7 +1746,7 @@ unsafe fn check_verified_properties(
         }
     };
 
-    if mimeparser.e2ee_helper.encrypted {
+    if !mimeparser.e2ee_helper.encrypted {
         verify_fail("This message is not encrypted".into());
         return 0;
     }