Bugfix/fix small bugs

[sebaleme]

2 small fixes. The first one is probably not affecting the binary, since the compiler optimizing non read data, and the second has a very restricted effect.

[StephenCWills]

The first one is probably not affecting the binary, since the compiler optimizing non read data

That's not correct. dmg was being used before your change, as it gets passed into ScaleSpellEffect(). Your compiler should be giving you a warning here.

[ 55%] Building CXX object Source/CMakeFiles/libdevilutionx.dir/missiles.cpp.o
.../DevilutionX/Source/missiles.cpp: In function ‘bool devilution::{anonymous}::GuardianTryFireAt(devilution::Missile&, devilution::Point)’:
.../DevilutionX/Source/missiles.cpp:729:23: warning: unused variable ‘player’ [-Wunused-variable]
  729 |         const Player &player = Players[missile._misource];
      |                       ^~~~~~
.../DevilutionX/Source/missiles.cpp:730:35: warning: ‘dmg’ may be used uninitialized [-Wmaybe-uninitialized]
  730 |         int dmg = ScaleSpellEffect(dmg, missile._mispllvl);
      |                   ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
.../DevilutionX/Source/missiles.cpp:730:13: note: ‘dmg’ was declared here
  730 |         int dmg = ScaleSpellEffect(dmg, missile._mispllvl);
      |             ^~~

[qndel]

I'd simply close this PR after reading title/description like this ...