bound shift width in dyncol integer readers

Noticed the dyncol integer readers shift by an exponent taken from the value length.

In dynamic_column_uint_read() the i*8 shift reaches 64 once a COLUMN_GET() blob gives an integer column more than 8 data bytes, and dynamic_column_var_uint_get() keeps shifting length*7 over a run of 0x80 continuation bytes (the charset id of a string value, intg/frac of a decimal). Both are undefined and abort under -fsanitize=shift. Reject the over-long integer and cap the varint at 10 groups.