Clear random data at the end in PixelStorage test.

The driver leaves garbage there and the test is failing.

src/Magnum/Test/PixelStorageGLTest.cpp

@@ -131,6 +131,11 @@ void PixelStorageGLTest::unpack2D() {
 
     MAGNUM_VERIFY_NO_ERROR();
 
+    /* Clear padding in the last row (the driver might leave them untouched,
+       confirmed on NVidia 355.11) */
+    CORRADE_VERIFY(actual.data().size() == Containers::ArrayView<const char>{ActualData}.size());
+    *(actual.data().end() - 1) = *(actual.data().end() - 2) = 0;
+
     CORRADE_COMPARE_AS(actual.data(), Containers::ArrayView<const char>{ActualData},
         TestSuite::Compare::Container);
 }