tesstrain.sh: Initialise fontconfig even if Arial isn't available

The fontconfig initialisation hardcodes using Arial. However it may
not be available, whereas the fonts being used later will be, so use
one of them for initialisation instead.

Author: nickjwhite

training/tesstrain_utils.sh

@@ -197,7 +197,7 @@ initialize_fontconfig() {
     local sample_path=${FONT_CONFIG_CACHE}/sample_text.txt
     echo "Text" >${sample_path}
     run_command ${TEXT2IMAGE_EXE} --fonts_dir=${FONTS_DIR} \
-        --font="Arial" --outputbase=${sample_path} --text=${sample_path} \
+        --font="${FONTS[0]}" --outputbase=${sample_path} --text=${sample_path} \
         --fontconfig_tmpdir=${FONT_CONFIG_CACHE}
 }