MDEC: Handle invalid commands

Fixes panic in Formula 1.

src/core/mdec.cpp

@@ -270,9 +270,9 @@ void MDEC::Execute()
             break;
 
           default:
-            Panic("Unknown command");
-            num_words = 0;
-            new_state = State::Idle;
+            Log_DevPrintf("Invalid MDEC command 0x%08X", cw.bits);
+            num_words = cw.parameter_word_count.GetValue();
+            new_state = State::NoCommand;
             break;
         }
 
@@ -334,6 +334,20 @@ void MDEC::Execute()
         continue;
       }
 
+      case State::NoCommand:
+      {
+        // can potentially have a large amount of halfwords, so eat them as we go
+        const u32 words_to_consume = std::min(m_remaining_halfwords, m_data_in_fifo.GetSize());
+        m_data_in_fifo.Remove(words_to_consume);
+        m_remaining_halfwords -= words_to_consume;
+        if (m_remaining_halfwords == 0)
+          goto finished;
+
+        m_state = State::Idle;
+        UpdateStatus();
+        continue;
+      }
+
       default:
         UnreachableCode();
         return;

src/core/mdec.h

@@ -56,7 +56,8 @@ private:
     DecodingMacroblock,
     WritingMacroblock,
     SetIqTable,
-    SetScaleTable
+    SetScaleTable,
+    NoCommand
   };
 
   union StatusRegister