Fix unnecessary exception use in 3 more methods (#8791)

Fix unnecessary exception use in 3 more methods (#8791)

* Fix unnecessary exception use in Server::SendBlocks

The code in this method calls getBlockNoCreate and then
messes around with try...catch to skip blocks which are not
in the memory. Additionally, it repeatedly calls
m_env.getMap() inside this loop. Speed the code up by
extracting the m_env.getMap() out of the loop and getting
rid of the try...catch.

* Fix unnecessary exception use in Server::SendBlock

Another unnecessary try...catch is slowing down
Server::SendBlock. Remove that to speed it up and get a nice
side effect of simplifying the code in question.

* Fix unnecessary exception use in MMVManip::initialEmerge

Remove another unneeded exception usage from
MMVManip::initialEmerge to speed that code up and simplify
it but be careful to not remove the braces as there is a
TimeTaker in use there.