Shaders: verify that no GL errors happened during construction.

src/Magnum/Shaders/Test/DistanceFieldVectorGLTest.cpp

@@ -55,6 +55,8 @@ void DistanceFieldVectorGLTest::construct2D() {
         #endif
         CORRADE_VERIFY(shader.validate().first);
     }
+
+    MAGNUM_VERIFY_NO_GL_ERROR();
 }
 
 void DistanceFieldVectorGLTest::construct3D() {
@@ -66,6 +68,8 @@ void DistanceFieldVectorGLTest::construct3D() {
         #endif
         CORRADE_VERIFY(shader.validate().first);
     }
+
+    MAGNUM_VERIFY_NO_GL_ERROR();
 }
 
 void DistanceFieldVectorGLTest::constructMove2D() {

src/Magnum/Shaders/Test/FlatGLTest.cpp

@@ -233,6 +233,8 @@ template<UnsignedInt dimensions> void FlatGLTest::construct() {
         #endif
         CORRADE_VERIFY(shader.validate().first);
     }
+
+    MAGNUM_VERIFY_NO_GL_ERROR();
 }
 
 template<UnsignedInt dimensions> void FlatGLTest::constructMove() {

src/Magnum/Shaders/Test/MeshVisualizerGLTest.cpp

@@ -62,6 +62,8 @@ void MeshVisualizerGLTest::construct() {
         #endif
         CORRADE_VERIFY(shader.validate().first);
     }
+
+    MAGNUM_VERIFY_NO_GL_ERROR();
 }
 
 #if !defined(MAGNUM_TARGET_GLES2) && !defined(MAGNUM_TARGET_WEBGL)

src/Magnum/Shaders/Test/PhongGLTest.cpp

@@ -345,6 +345,8 @@ void PhongGLTest::construct() {
         #endif
         CORRADE_VERIFY(shader.validate().first);
     }
+
+    MAGNUM_VERIFY_NO_GL_ERROR();
 }
 
 void PhongGLTest::constructMove() {

src/Magnum/Shaders/Test/VectorGLTest.cpp

@@ -55,6 +55,8 @@ void VectorGLTest::construct2D() {
         #endif
         CORRADE_VERIFY(shader.validate().first);
     }
+
+    MAGNUM_VERIFY_NO_GL_ERROR();
 }
 
 void VectorGLTest::construct3D() {
@@ -66,6 +68,8 @@ void VectorGLTest::construct3D() {
         #endif
         CORRADE_VERIFY(shader.validate().first);
     }
+
+    MAGNUM_VERIFY_NO_GL_ERROR();
 }
 
 void VectorGLTest::constructMove2D() {

src/Magnum/Shaders/Test/VertexColorGLTest.cpp

@@ -55,6 +55,8 @@ void VertexColorGLTest::construct2D() {
         #endif
         CORRADE_VERIFY(shader.validate().first);
     }
+
+    MAGNUM_VERIFY_NO_GL_ERROR();
 }
 
 void VertexColorGLTest::construct3D() {
@@ -66,6 +68,8 @@ void VertexColorGLTest::construct3D() {
         #endif
         CORRADE_VERIFY(shader.validate().first);
     }
+
+    MAGNUM_VERIFY_NO_GL_ERROR();
 }
 
 void VertexColorGLTest::constructMove2D() {