Windows: If a font supports a script, but not an individiual glyph in the font, search for the glyph in all fonts until it is found

Sometimes Qt on Windows will register that a font supports a specific script even when it doesn't. An example is the Segoe UI font which reports to contain glyphs in the thai unicode range because it has the currency symbol for Baht.

When this occurs, Qt may select the wrong font to display the text from the writing system, and when the lookup of the individual character fails, it will look through a short list of alternatives. When using font config on Linux, however, we will do this search in all the system fonts, because font config supports an iterative font lookup mechanism. We should do something similar on Windows when the glyph is not found in the short list.

Be careful to keep the overhead down, since this can affect both memory footprint and start-up time (only in cases where you would otherwise see boxes in the text.)