Fix segfault on determining reactionfire mode
Upstream commit:
https://github.com/ufoaiorg/ufoai/commit/1258171073b5049c5699c80bbfad52362b4f3b80

Index: src/game/inv_shared.cpp
--- src/game/inv_shared.cpp.orig
+++ src/game/inv_shared.cpp
@@ -633,9 +633,6 @@ const fireDef_t* Item::getSlowestFireDef () const
  */
 const objDef_t* Item::getReactionFireWeaponType () const
 {
-	if (!this)
-		return nullptr;
-
 	if (def()) {
 		const fireDef_t* fd = getFiredefs();
 		if (fd && fd->reaction)
@@ -999,9 +996,9 @@ Item* Inventory::findInContainer (const containerIndex
  */
 bool Inventory::holdsReactionFireWeapon () const
 {
-	if (getRightHandContainer()->getReactionFireWeaponType())
+	if (getRightHandContainer() != nullptr && getRightHandContainer()->getReactionFireWeaponType())
 		return true;
-	if (getLeftHandContainer()->getReactionFireWeaponType())
+	if (getLeftHandContainer() != nullptr && getLeftHandContainer()->getReactionFireWeaponType())
 		return true;
 	return false;
 }
