Draw 16, not 15 characters max in the OSK.

This is a convenient number because passwords in some games are 16
characters long.  16 seems more likely to be choosen by developers as a
limit, and still fits well enough within the bounds.

Core/Dialog/PSPOskDialog.cpp

@@ -706,7 +706,7 @@ void PSPOskDialog::RenderKeyboard()
 
 	std::string buffer;
 
-	u32 FIELDDRAWMAX = 15;
+	static const u32 FIELDDRAWMAX = 16;
 	u32 limit = FieldMaxLength();
 	u32 drawLimit = std::min(FIELDDRAWMAX, limit);   // Field drew length limit.