gcc 11.2 compilation warning due to snprintf buffer size

[chrisguiney]

I believe the condition was present since initially introduced with 45406d4

It seems like the buffer is too small for the largest potential output. I believe this is a warning in gcc, but it's only sane to compile with -Werror

cd /home/chris/cgrt/build/ext/nanogui && /usr/bin/c++ -DNANOGUI_BUILD -DNANOGUI_SHARED -DNANOGUI_USE_OPENGL -DNVG_BUILD -DNVG_SHARED -DNVG_STB_IMAGE_IMPLEMENTATION -D_GLFW_BUILD_DLL -I/home/chris/cgrt/build/ext/nanogui -I/home/chris/cgrt/ext/nanogui/include -I/home/chris/cgrt/ext/nanogui/ext/nanovg/src -I/home/chris/cgrt/ext/nanogui/ext/glfw/include -Wall -Wextra -g -ggdb -Og -Wall -Werror -fpermissive -fPIC -fvisibility=hidden -march=nehalem -MD -MT ext/nanogui/CMakeFiles/nanogui.dir/src/layout.cpp.o -MF CMakeFiles/nanogui.dir/src/layout.cpp.o.d -o CMakeFiles/nanogui.dir/src/layout.cpp.o -c /home/chris/cgrt/ext/nanogui/src/layout.cpp
In file included from /home/chris/cgrt/ext/nanogui/src/layout.cpp:14:
/home/chris/cgrt/ext/nanogui/include/nanogui/layout.h: In member function ‘nanogui::AdvancedGridLayout::Anchor::operator std::string() const’:
/home/chris/cgrt/ext/nanogui/include/nanogui/layout.h:411:77: error: ‘, ’ directive output may be truncated writing 2 bytes into a region of size between 0 and 10 [-Werror=format-truncation=]
  411 |             snprintf(buf, 50, "Format[pos=(%i, %i), size=(%i, %i), align=(%i, %i)]",
      |                                                                             ^~
/home/chris/cgrt/ext/nanogui/include/nanogui/layout.h:411:31: note: directive argument in the range [0, 255]
  411 |             snprintf(buf, 50, "Format[pos=(%i, %i), size=(%i, %i), align=(%i, %i)]",
      |                               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/stdio.h:894,
                 from /usr/include/c++/11/cstdio:42,
                 from /usr/include/c++/11/ext/string_conversions.h:43,
                 from /usr/include/c++/11/bits/basic_string.h:6608,
                 from /usr/include/c++/11/string:55,
                 from /home/chris/cgrt/ext/nanogui/include/nanogui/common.h:21,
                 from /home/chris/cgrt/ext/nanogui/include/nanogui/object.h:15,
                 from /home/chris/cgrt/ext/nanogui/include/nanogui/layout.h:18,
                 from /home/chris/cgrt/ext/nanogui/src/layout.cpp:14:
/usr/include/x86_64-linux-gnu/bits/stdio2.h:71:35: note: ‘__builtin___snprintf_chk’ output between 46 and 58 bytes into a destination of size 50
   71 |   return __builtin___snprintf_chk (__s, __n, __USE_FORTIFY_LEVEL - 1,
      |          ~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   72 |                                    __glibc_objsize (__s), __fmt,
      |                                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   73 |                                    __va_arg_pack ());
      |                                    ~~~~~~~~~~~~~~~~~
cc1plus: all warnings being treated as errors
gmake[3]: *** [ext/nanogui/CMakeFiles/nanogui.dir/build.make:223: ext/nanogui/CMakeFiles/nanogui.dir/src/layout.cpp.o] Error 1
gmake[3]: Leaving directory '/home/chris/cgrt/build'
gmake[2]: *** [CMakeFiles/Makefile2:416: ext/nanogui/CMakeFiles/nanogui.dir/all] Error 2
gmake[2]: Leaving directory '/home/chris/cgrt/build'
gmake[1]: *** [CMakeFiles/Makefile2:790: src/cgrt-cuda/CMakeFiles/cgrt-cuda.dir/rule] Error 2
gmake[1]: Leaving directory '/home/chris/cgrt/build'
gmake: *** [Makefile:377: cgrt-cuda] Error 2