DebugTools: fix textureSubImage() for float textures on ES3.

By accident the returned image had zero size.

doc/changelog.dox

@@ -137,6 +137,8 @@ See also:
     @gl_extension{EXT,instanced_arrays}, @gl_extension{EXT,draw_instanced},
     @gl_extension{NV,instanced_arrays} and @gl_extension{NV,draw_instanced}
     extensions
+-   Reading of float textures on ES3 contexts using
+    @ref DebugTools::textureSubImage() returned a zero-sized image by accident
 -   Updated the `base-qt` bootstrap project to correctly reset state tracker
     when going from and back to Qt code, and to use the framebuffer provided by
     Qt instead of @ref GL::defaultFramebuffer (see

src/Magnum/DebugTools/TextureImage.cpp

@@ -152,7 +152,7 @@ void textureSubImage(GL::Texture2D& texture, const Int level, const Range2Di& ra
         const Vector2i imageSize = image.size();
         Image2D temp{image.storage(), reinterpretFormat, GL::PixelType::UnsignedInt, imageSize, image.release()};
         fb.read(range, temp);
-        image = Image2D{image.storage(), image.format(), image.formatExtra(), image.pixelSize(), imageSize, temp.release()};
+        image = Image2D{image.storage(), image.format(), image.formatExtra(), image.pixelSize(), range.size(), temp.release()};
         return;
     }
     #endif