Eliminate 'possible loss of data' compiler warnings in cord (MS VC)

Eliminate 'possible loss of data' compiler warnings in cord (MS VC)
(Cherry-pick commit 1060ec9 from 'release-7_6' branch.)

* cord/cordbscs.c (CORD_cat_char_star, CORD_cat, CORD_from_fn_inner):
Add explicit cast in assignment of result->depth, result->len.
* cord/cordbscs.c (CORD_substr_checked): Change type of "j", "lim"
local variables from int to size_t.
* cord/cordbscs.c (CORD_init_min_len): Add explicit cast (to int) in
assignment of CORD_max_len.
* cord/cordxtra.c (CORD_ncmp): Add explicit cast (to long) when "avail"
local variable is updated.
* cord/cordxtra.c (CORD_chr, CORD_rchr, CORD_from_file_eager): Add
explicit cast to char (from int) for "c" local variable in assignment
of d.target and in CORD_ec_append call.
* cord/cordxtra.c (refill_cache): Add explicit cast to long (from
size_t) for line_start in fseek call.
* cord/tests/de.c (line_pos, fix_pos, do_command): Add explicit cast to
int in assignment of *c, line, col.
* cord/tests/de.c (do_command): Reset line, col and file_pos variables
(of different types) in separate statements.
* cord/tests/de_win.c (WinMain): Add explicit cast of msg.wParam to int
in return statement.