Always load unifont as a fallback

This prevents users from shooting themselves in the foot by selecting a
different font and removing unifont from their font list

src/font_loader.h

@@ -2,6 +2,7 @@
 #ifndef FONT_LOADER_H
 #define FONT_LOADER_H
 
+#include <algorithm>
 #include <fstream>
 #include <stdexcept>
 #include <string>
@@ -51,6 +52,17 @@ class font_loader
                 } else {
                     config.read( "overmap_typeface", overmap_typeface );
                 }
+
+                // Ensure that unifont is always loaded as a fallback font to prevent users from shooting themselves in the foot
+                auto ensure_unifont_loaded = []( std::vector<std::string> &font_list ) {
+                    if( std::find( std::begin( font_list ), std::end( font_list ), "unifont" ) == font_list.end() ) {
+                        font_list.emplace_back( "unifont" );
+                    }
+                };
+                ensure_unifont_loaded( typeface );
+                ensure_unifont_loaded( map_typeface );
+                ensure_unifont_loaded( overmap_typeface );
+
             } catch( const std::exception &err ) {
                 throw std::runtime_error( std::string( "loading font settings from " ) + path + " failed: " +
                                           err.what() );