Fix skill fail packet handling causing nullptr crash when switching characters

How to reproduce: spam emote then quickly switch char

Thread 1 "manaplus" received signal SIGSEGV, Segmentation fault.
SkillDialog::getSkill (this=0x0, id=id@entry=1) at gui/windows/skilldialog.cpp:805

0  SkillDialog::getSkill (this=0x0, id=id@entry=1) at gui/windows/skilldialog.cpp:805
1  EAthena::SkillRecv::processSkillFailed (msg=...) at net/eathena/skillrecv.cpp:302
...

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mana/plus!92

1 files changed, 6 insertions, 2 deletions

diff --git a/src/net/eathena/skillrecv.cpp b/src/net/eathena/skillrecv.cpp
index 3f3e8efb1..dc24b15b4 100644
--- a/src/net/eathena/skillrecv.cpp
+++ b/src/net/eathena/skillrecv.cpp
@@ -298,7 +298,9 @@ void SkillRecv::processSkillFailed(Net::MessageIn &msg)
             localPlayer->stopAdvert();
         }
 
-        const SkillInfo *const info = skillDialog->getSkill(bskill);
+        const SkillInfo *const info = skillDialog
+                                    ? skillDialog->getSkill(bskill)
+                                    : nullptr;
         if (info != nullptr)
         {
             txt = info->errorText;
@@ -311,7 +313,9 @@ void SkillRecv::processSkillFailed(Net::MessageIn &msg)
     }
     else
     {
-        const SkillInfo *const info = skillDialog->getSkill(skillId);
+        const SkillInfo *const info = skillDialog
+                                    ? skillDialog->getSkill(skillId)
+                                    : nullptr;
         if (info != nullptr)
         {
             txt = info->errorText + ".";