Math: make Vector::pad() default argument work with Half.

Got lucky enough that the default zero-initialization constructor does
exactly what I need. Otherwise ugh I don't know what I would do.

src/Magnum/Math/Test/VectorTest.cpp

@@ -27,6 +27,7 @@
 #include <Corrade/TestSuite/Tester.h>
 #include <Corrade/Utility/DebugStl.h>
 
+#include "Magnum/Math/Half.h"
 #include "Magnum/Math/Vector.h"
 #include "Magnum/Math/StrictWeakOrdering.h"
 
@@ -58,6 +59,7 @@ struct VectorTest: Corrade::TestSuite::Tester {
     void construct();
     void constructFromData();
     void constructPad();
+    void constructPadDefaultHalf();
     void constructDefault();
     void constructNoInit();
     void constructOneValue();
@@ -118,14 +120,17 @@ struct VectorTest: Corrade::TestSuite::Tester {
 typedef Math::Constants<Float> Constants;
 typedef Math::Rad<Float> Rad;
 typedef Vector<2, Float> Vector2;
+typedef Vector<2, Half> Vector2h;
 typedef Vector<3, Float> Vector3;
 typedef Vector<4, Float> Vector4;
+typedef Vector<4, Half> Vector4h;
 typedef Vector<4, Int> Vector4i;
 
 VectorTest::VectorTest() {
     addTests({&VectorTest::construct,
               &VectorTest::constructFromData,
               &VectorTest::constructPad,
+              &VectorTest::constructPadDefaultHalf,
               &VectorTest::constructDefault,
               &VectorTest::constructNoInit,
               &VectorTest::constructOneValue,
@@ -207,6 +212,13 @@ void VectorTest::constructPad() {
     CORRADE_COMPARE(e, Vector4(1.0f, -1.0f, 8.0f, 2.3f));
 }
 
+void VectorTest::constructPadDefaultHalf() {
+    using namespace Literals;
+    /* The default pad value should work also for the Half type */
+    Vector4h a = Vector4h::pad(Vector2h{1.0_h, -1.0_h});
+    CORRADE_COMPARE(a, (Vector4h{1.0_h, -1.0_h, 0.0_h, 0.0_h}));
+}
+
 void VectorTest::constructDefault() {
     constexpr Vector4 a;
     constexpr Vector4 b{ZeroInit};

src/Magnum/Math/Vector.h

@@ -166,7 +166,7 @@ template<std::size_t size, class T> class Vector {
          * with @p value, otherwise it's cut.
          * @see @ref Vector4::pad(const Vector<otherSize, T>&, T, T)
          */
-        template<std::size_t otherSize> constexpr static Vector<size, T> pad(const Vector<otherSize, T>& a, T value = T(0)) {
+        template<std::size_t otherSize> constexpr static Vector<size, T> pad(const Vector<otherSize, T>& a, T value = T()) {
             return padInternal<otherSize>(typename Implementation::GenerateSequence<size>::Type(), a, value);
         }
 
@@ -1248,7 +1248,7 @@ extern template MAGNUM_EXPORT Corrade::Utility::Debug& operator<<(Corrade::Utili
     static const Type<T>& from(const T* data) {                             \
         return *reinterpret_cast<const Type<T>*>(data);                     \
     }                                                                       \
-    template<std::size_t otherSize> constexpr static Type<T> pad(const Math::Vector<otherSize, T>& a, T value = T(0)) { \
+    template<std::size_t otherSize> constexpr static Type<T> pad(const Math::Vector<otherSize, T>& a, T value = T()) { \
         return Math::Vector<size, T>::pad(a, value);                        \
     }                                                                       \
                                                                             \