Attempt to address CI failures in #3061

- Install libpng-dev on Linux GCC workflow so that mrconvert tests involving the PNG format can succeed.
- Modify DEBUG call in ImageIO::PNG::load(): concatenation of an empty string seemingly causing a string overflow when compiling on Windows.

Author: Lestropie

.github/workflows/checks.yml

@@ -90,7 +90,7 @@ jobs:
     - name: install dependencies
       run: |
          sudo apt-get update
-         sudo apt-get install g++-9 qt6-base-dev libglvnd-dev zlib1g-dev libfftw3-dev ninja-build python3-numpy
+         sudo apt-get install g++-9 qt6-base-dev libglvnd-dev zlib1g-dev libfftw3-dev ninja-build python3-numpy libpng-dev
 
     - name: Run sccache-cache
       uses: mozilla-actions/[email protected]

cpp/core/image_io/png.cpp

@@ -25,7 +25,9 @@
 namespace MR::ImageIO {
 
 void PNG::load(const Header &header, size_t) {
-  DEBUG(std::string("loading PNG image") + (files.size() > 1 ? "s" : "") + " \"" + header.name() + "\"");
+  DEBUG(std::string("loading PNG ")               //
+        + (files.size() > 1 ? "images" : "image") //
+        + " \"" + header.name() + "\"");          //
   segsize = (header.datatype().bits() * voxel_count(header) + 7) / 8;
   addresses.resize(1);
   addresses[0].reset(new uint8_t[segsize]);