imap-send.c: more style fixes

The previous one sqeezed unnecessary whitespaces and joined function type
and name in the definition split across lines.  This patch further fixes
many remaining style issues:

 - We are not particularly fond of typedef to hide the underlying struct
   definitions.

 - Asterisk comes next variable, i.e. "type *var", not "type * var" nor
   "type* var".

 - Casting to pointer to a type is "(type *)", not "(type*)".

 - An open brace comes on the same line as closing parenthesis of "if (...)"
   condition; "else" comes on the same line as closing brace of its
   corresponding "if (...) {".

 - Avoid single liner "if (...) <stmt>;"; they should be on two separate
   lines.

Signed-off-by: Junio C Hamano <gitster@pobox.com>