[EAX] Fix error handling (#953)

- Set error on EAX call failure if context is available.
- Reset error on successful retreiving the last error code.

Reference: EAX 4.0 - Programmer's Guide (pg.37)

al/eax/api.h

@@ -362,6 +362,7 @@ constexpr auto EAXCONTEXT_MINMACROFXFACTOR = 0.0F;
 constexpr auto EAXCONTEXT_MAXMACROFXFACTOR = 1.0F;
 constexpr auto EAXCONTEXT_DEFAULTMACROFXFACTOR = 0.0F;
 
+constexpr auto EAXCONTEXT_DEFAULTLASTERROR = EAX_OK;
 
 extern const GUID EAXPROPERTYID_EAX40_FXSlot0;
 extern const GUID EAXPROPERTYID_EAX50_FXSlot0;

alc/context.cpp

@@ -586,7 +586,7 @@ void ALCcontext::eax_update_speaker_configuration()
 
 void ALCcontext::eax_set_last_error_defaults() noexcept
 {
-    mEaxLastError = EAX_OK;
+    mEaxLastError = EAXCONTEXT_DEFAULTLASTERROR;
 }
 
 void ALCcontext::eax_session_set_defaults() noexcept
@@ -675,6 +675,7 @@ void ALCcontext::eax_get_misc(const EaxCall& call)
         break;
     case EAXCONTEXT_LASTERROR:
         call.set_value<ContextException>(mEaxLastError);
+        mEaxLastError = EAX_OK;
         break;
     case EAXCONTEXT_SPEAKERCONFIG:
         call.set_value<ContextException>(mEaxSpeakerConfig);
@@ -1045,6 +1046,7 @@ try
 }
 catch(...)
 {
+    context->eaxSetLastError();
     eax_log_exception(__func__);
     return AL_INVALID_OPERATION;
 }
@@ -1072,6 +1074,7 @@ try
 }
 catch(...)
 {
+    context->eaxSetLastError();
     eax_log_exception(__func__);
     return AL_INVALID_OPERATION;
 }