Fix smart wrap in pager without breaking header

Fix smart wrap in pager without breaking header

This commit addresses the issue of smart wrap not working if a line
started with whitespace.

This behavior was a result commit f5e472b where smart wrap was disabled
on lines beginning with a space or tab to prevent headers from having
weird wrapping.

This commit addresses this issue by only applying smart wrapping if the
pager is displaying a message body. This allows smart_wrap to work
inside of a message and preserves what commit f5e472b addressed.

Additionally, the buf[cnt] checks have been simplified with the use of
the ISSPACE() macro.

While fixing the smart wrap, it became apparent that the HEADER portion
of the pager was not properly updating when the wrap size was modified.
To address this, the wrap command was changed from R_PAGER to
R_PAGER_FLOW in init.h. This redraws the pager after wrap is modified.