Fix FTBFS with GCC6

Signed-off-by: Slávek Banko <slavek.banko@axis.cz>

src/gui/editors/notation/NoteFontMap.cpp

@@ -785,11 +785,11 @@ const
 {
     SymbolDataMap::const_iterator i = m_data.find(charName);
     if (i == m_data.end())
-        return false;
+        return 0;
 
     SizeDataMap::const_iterator si = m_sizes.find(size);
     if (si == m_sizes.end())
-        return false;
+        return 0;
 
     int fontId = i->second.getFontId();
 
@@ -802,7 +802,7 @@ const
 
     SystemFontNameMap::const_iterator fni = m_systemFontNames.find(fontId);
     if (fontId < 0 || fni == m_systemFontNames.end())
-        return false;
+        return 0;
     TQString fontName = fni->second;
 
     CharBaseMap::const_iterator bi = m_bases.find(fontId);