[Test] (Pipe): pin the pre-fill window - every stamp of 0 is stale at serial 0, a read before any fill aborts naming "<none>", and the FATAL=0 child leaves through std::exit so the teardown summary is observed

- PipeCatalogue.PipeInputFieldsStartUnfilled asserted "unfilled" only after setting the serial to 1 by hand, stepping around the serial-0 window; it now asserts every field stale on a value-initialised state first (sticky fields included).
- PipeInputsTest.ReadingBeforeAnyFillAbortsNamingNoVerb: a live context, no fill, gPipeInputs.GetLineWidth() in a forked child; the parent expects SIGABRT, exactly Fatal{UnmigratedPipeInput, "GetLineWidth@<none>"}, no PipeVerifyDiffer and no arming line. In a verify build the child sets Features.PipeVerify first, the lane's shape.
- VerifyFatalOffLogsTheDivergenceAndContinues: the child _exit(0)ed, so VerifyState's destructor never ran and the "verify summary" line was covered only by a lane run; std::exit(0) runs it, and the parent now asserts "2 divergence(s) survived MOBILEGL_PIPE_VERIFY_FATAL=0".

MobileGL/MG_Test/Pipe/PipeCatalogueTest.cpp

@@ -225,6 +225,12 @@ TEST(PipeCatalogue, CoverageAccountsForEveryInventoryRow) {
 TEST(PipeCatalogue, PipeInputFieldsStartUnfilled) {
     EXPECT_EQ(kMGPipeInputFieldCount, 63u);
     MGPipeFilledState state{};
+    // Before the first fill the serial is 0 as well: 0 == 0 must not read as fresh, on the
+    // sticky branch either (the window D6 names "<Field>@<none>").
+    EXPECT_EQ(state.CurrentVerbSerial, 0u);
+    for (SizeT f = 0; f < kMGPipeInputFieldCount; ++f) {
+        EXPECT_FALSE(MGPipeInputFieldIsFresh(state, static_cast<MGPipeInputField>(f))) << kMGPipeInputFieldNames[f];
+    }
     state.CurrentVerbSerial = 1;
     EXPECT_FALSE(MGPipeInputFieldIsFresh(state, MGPipeInputField::GetRenderStateParameters));
     state.FilledGen[static_cast<SizeT>(MGPipeInputField::GetRenderStateParameters)] = 1;