Review feedback from @Bronek

- Exclude impossible logging from code coverage, too.

src/xrpld/app/tx/detail/Transactor.cpp

@@ -237,11 +237,11 @@ Transactor::preflight2(PreflightContext const& ctx)
         auto const sigValid = checkValidity(
             ctx.app.getHashRouter(), ctx.tx, ctx.rules, ctx.app.config());
         if (sigValid.first == Validity::SigBad)
-        {
+        {  // LCOV_EXCL_START
             JLOG(ctx.j.debug())
                 << "preflight2: bad signature. " << sigValid.second;
-            return temINVALID;  // LCOV_EXCL_LINE
-        }
+            return temINVALID;
+        }  // LCOV_EXCL_STOP
     }
     return tesSUCCESS;
 }