Fix /setspeedmod: apply per-character, persist across stat recalculation

Previously stomped the shared GServer->MOVE_SPEED_MOD movement-timing
divisor, which character.cpp's UpdatePosition also uses for monster position
interpolation -- GM testing broke movement/attack range server-wide until
restart. Now stores a per-character SpeedModPercent that GetMoveSpeed()
applies on every recompute, so it survives future SetStats() calls instead
of being silently overwritten back to base speed. Also fixes Mspd_base (the
value actually broadcast to clients) never being set while WALKING.

Src/World Server/playerstats.cpp

@@ -1050,6 +1050,13 @@ unsigned int CPlayer::GetMoveSpeed( )
         default:
         break;
     }
+    if(Stats->SpeedModPercent != 100)
+        mspeed = mspeed * Stats->SpeedModPercent / 100;
+    // Mspd_base (what actually gets broadcast to clients, e.g. worldpackets.cpp's
+    // 0x782) was previously only touched by the RUNNING/DRIVING branches above --
+    // WALKING/default left it stale, so speed changes never showed up client-side
+    // while walking. Mirror the final value unconditionally.
+    Stats->Mspd_base = mspeed;
     return mspeed;
 }