Added New Exception

Author: Laky-64

config.xml

@@ -144,6 +144,8 @@
   <option id="CALL_EXCEPTIONS">
     <category-title>exception <ref>pytgcalls.exceptions.<sb>CallDeclined</sb></ref></category-title>
     <subtext><text>The call was declined by the user.</text></subtext>
+    <category-title>exception <ref>pytgcalls.exceptions.<sb>CallBusy</sb></ref></category-title>
+    <subtext><text>When the user is already in a call.</text></subtext>
     <category-title>exception <ref>pytgcalls.exceptions.<sb>CallDiscarded</sb></ref></category-title>
     <subtext><text>The call was discarded by the user while connecting.</text></subtext>
     <config id="TELEGRAM_EXCEPTION"/>