MeshTools: ensure proper assert is printed in compressIndices().

src/Magnum/MeshTools/CompressIndices.cpp

@@ -165,9 +165,12 @@ Trade::MeshData compressIndices(Trade::MeshData&& data, MeshIndexType atLeast) {
 }
 
 Trade::MeshData compressIndices(const Trade::MeshData& data, MeshIndexType atLeast) {
+    CORRADE_ASSERT(data.isIndexed(), "MeshTools::compressIndices(): mesh data not indexed", (Trade::MeshData{MeshPrimitive::Triangles, 0}));
+
     return compressIndices(Trade::MeshData{data.primitive(),
         {}, data.indexData(), Trade::MeshIndexData{data.indices()},
-        {}, data.vertexData(), Trade::meshAttributeDataNonOwningArray(data.attributeData())}, atLeast);
+        {}, data.vertexData(), Trade::meshAttributeDataNonOwningArray(data.attributeData()),
+        data.vertexCount()}, atLeast);
 }
 
 #ifdef MAGNUM_BUILD_DEPRECATED

src/Magnum/MeshTools/Test/CompressIndicesTest.cpp

@@ -316,10 +316,14 @@ void CompressIndicesTest::compressMeshDataMove() {
 }
 
 void CompressIndicesTest::compressMeshDataNonIndexed() {
+    /* Test both r-value and l-value overload */
     std::ostringstream out;
     Error redirectError{&out};
+    Trade::MeshData mesh{MeshPrimitive::TriangleFan, 5};
+    MeshTools::compressIndices(mesh);
     MeshTools::compressIndices(Trade::MeshData{MeshPrimitive::TriangleFan, 5});
     CORRADE_COMPARE(out.str(),
+        "MeshTools::compressIndices(): mesh data not indexed\n"
         "MeshTools::compressIndices(): mesh data not indexed\n");
 }