[AD] Allegro font grabber bug

["Peter Hull" <Peter.Hull@xxxxxxxxxx>]

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\uc1\pard\f0\fs20 Dear Conductors,\par
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I have found that the grabber can crash when you try to grab a font from a bitmap, if the character cell heights are not all the same.\par
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The font plug-in accesses bitmap data directly and this can step outside the bounds of the bitmap. If you replace the direct access with a call to 'getpixel' it doesn't crash.\par
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I can send you a diff for this, if you tell me what format you want.\par
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I am using WIP 3.9.26, djgpp version, under DOS.\par
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Yours,\par
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Pete\par
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