Fix font clearing

Author: mdboom

src/ft2font.cpp

@@ -68,13 +68,16 @@ void FT2Image::resize(long width, long height)
             delete[] m_buffer;
             m_buffer = NULL;
             m_buffer = new unsigned char[numBytes];
-            memset(m_buffer, 0, numBytes);
         }
 
         m_width = (unsigned long)width;
         m_height = (unsigned long)height;
     }
 
+    if (numBytes && m_buffer) {
+        memset(m_buffer, 0, numBytes);
+    }
+
     m_dirty = true;
 }