tif_getimage.c: Fix buffer underflow crash for less raster rows at TIFFReadRGBAImageOriented()

Su Lausrequested to merge
Su_Laus/libtiff:fix_704_TIFFReadRGBAImage_crash into master

tif_getimage.c: Fix buffer underflow crash if number of raster rows are less than available strip image rows and harmonize behaviour of TIFFRGBAImageGet() and TIFFReadRGBAImageOriented().

Closes #704 (closed)

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