Loader: Update iterator for loop

[ma8ma]

for文によるイテレーターの走査処理をSTLアルゴリズム関数や範囲ベースfor文に更新して保守性を向上させます。

関連のpull request: #783

[ma8ma]

gcc-6でエラー

https://github.com/JDimproved/JDim/runs/3989116591?check_suite_focus=true

g++-6 -Isrc/jdlib/ba3c4f7@@jdlib@sta -Isrc/jdlib -I../src/jdlib -Isrc/jdlib/.. -I../src/jdlib/.. -I/usr/include/gtkmm-3.0 -I/usr/lib/x86_64-linux-gnu/gtkmm-3.0/include -I/usr/include/atkmm-1.6 -I/usr/include/gtk-3.0/unix-print -I/usr/include/gdkmm-3.0 -I/usr/lib/x86_64-linux-gnu/gdkmm-3.0/include -I/usr/include/giomm-2.4 -I/usr/lib/x86_64-linux-gnu/giomm-2.4/include -I/usr/include/pangomm-1.4 -I/usr/lib/x86_64-linux-gnu/pangomm-1.4/include -I/usr/include/glibmm-2.4 -I/usr/lib/x86_64-linux-gnu/glibmm-2.4/include -I/usr/include/at-spi2-atk/2.0 -I/usr/include/at-spi-2.0 -I/usr/include/dbus-1.0 -I/usr/lib/x86_64-linux-gnu/dbus-1.0/include -I/usr/include/gtk-3.0 -I/usr/include/gio-unix-2.0/ -I/usr/include/harfbuzz -I/usr/include/pango-1.0 -I/usr/include/atk-1.0 -I/usr/include/cairomm-1.0 -I/usr/lib/x86_64-linux-gnu/cairomm-1.0/include -I/usr/include/cairo -I/usr/include/pixman-1 -I/usr/include/freetype2 -I/usr/include/sigc++-2.0 -I/usr/lib/x86_64-linux-gnu/sigc++-2.0/include -I/usr/include/gdk-pixbuf-2.0 -I/usr/include/libpng16 -I/usr/include/glib-2.0 -I/usr/lib/x86_64-linux-gnu/glib-2.0/include -I/usr/include/p11-kit-1 -fdiagnostics-color=always -pipe -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -Wnon-virtual-dtor -Wextra -Wpedantic -std=c++1z -g -DHAVE_CONFIG_H=1 '-DGTK_DOMAIN="gtk30"' -Wno-unused-parameter -D_DEBUG -fPIC -pthread  -MD -MQ 'src/jdlib/ba3c4f7@@jdlib@sta/loader.cpp.o' -MF 'src/jdlib/ba3c4f7@@jdlib@sta/loader.cpp.o.d' -o 'src/jdlib/ba3c4f7@@jdlib@sta/loader.cpp.o' -c ../src/jdlib/loader.cpp
../src/jdlib/loader.cpp: In function ‘bool JDLIB::get_token(JDLIB::Loader*)’:
../src/jdlib/loader.cpp:100:52: error: binding ‘const string {aka const std::__cxx11::basic_string<char>}’ to reference of type ‘std::__cxx11::basic_string<char>&’ discards qualifiers
     const auto compare_host = [&h = loader->data().host]( const auto* ldr ) { return ldr && ldr->data().host == h; };
                                     ~~~~~~~~~~~~~~~^~~~