Fix another crash due to incorrect hash value of glyph rows, bug #10035.

Fix another crash due to incorrect hash value of glyph rows, bug #10035.

 src/dispnew.c (swap_glyph_pointers): Swap the used[] arrays and the
 hash values of the two rows.
 (copy_row_except_pointers): Preserve the used[] arrays and the
 hash values of the two rows.
 src/xdisp.c (row_hash): New function, body extracted from
 compute_line_metrics.
 (compute_line_metrics): Call row_hash, instead of computing the
 hash code inline.
 src/dispnew.c (verify_row_hash): Call row_hash for computing the
 hash code of a row, instead of duplicating code from xdisp.c.
 src/dispextern.h (row_hash): Add prototype.