Make ManagedBackendTexture fail on invalid GrBackendTexture

Makes it more sensible.

A bunch of call sites we're already written to expect this. Update
some others.

Change-Id: I77c28045ebf01e6aa9d92d2ebc37287604ec10c9
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/332544
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
diff --git a/tests/GrPorterDuffTest.cpp b/tests/GrPorterDuffTest.cpp
index c7f2a44..0adb595 100644
--- a/tests/GrPorterDuffTest.cpp
+++ b/tests/GrPorterDuffTest.cpp
@@ -1001,6 +1001,10 @@
 
     auto mbet = sk_gpu_test::ManagedBackendTexture::MakeWithoutData(
             ctx, 100, 100, kRGBA_8888_SkColorType, GrMipmapped::kNo, GrRenderable::kNo);
+    if (!mbet) {
+        ERRORF(reporter, "Could not make texture.");
+        return;
+    }
     GrXferProcessor::DstProxyView fakeDstProxyView;
     {
         sk_sp<GrTextureProxy> proxy = proxyProvider->wrapBackendTexture(