SharedFontState: Add 'defaultFontFamily' property

Some scripts may end up ignoring RGSS-side defaults and just
requesting invalid / empty family names; in this case
the internal default family will be substituted.

src/font.cpp

@@ -27,6 +27,7 @@
 #include "boost-hash.h"
 #include "util.h"
 #include "config.h"
+#include "debugwriter.h"
 
 #include <string>
 #include <utility>
@@ -77,6 +78,10 @@ struct SharedFontStatePrivate
 	/* Pool of already opened fonts; once opened, they are reused
 	 * and never closed until the termination of the program */
 	BoostHash<FontKey, TTF_Font*> pool;
+
+	/* Internal default font family that is used anytime an
+	 * empty/invalid family is requested */
+	std::string defaultFamily;
 };
 
 SharedFontState::SharedFontState(const Config &conf)
@@ -132,6 +137,11 @@ void SharedFontState::initFontSetCB(SDL_RWops &ops,
 _TTF_Font *SharedFontState::getFont(std::string family,
                                     int size)
 {
+	if (family.empty()) {
+		Debug() << "Invalid font family" << family << "requested, substituting internal default";
+		family = p->defaultFamily;
+	}
+
 	/* Check for substitutions */
 	if (p->subs.contains(family))
 		family = p->subs[family];
@@ -202,6 +212,11 @@ _TTF_Font *SharedFontState::openBundled(int size)
 	return TTF_OpenFontRW(ops, 1, size);
 }
 
+void SharedFontState::setDefaultFontFamily(const std::string &family)
+{
+	p->defaultFamily = family;
+}
+
 void pickExistingFontName(const std::vector<std::string> &names,
                           std::string &out,
                           const SharedFontState &sfs)

src/font.h

@@ -54,6 +54,8 @@ public:
 
 	static _TTF_Font *openBundled(int size);
 
+	void setDefaultFontFamily(const std::string &family);
+
 private:
 	SharedFontStatePrivate *p;
 };