Common/coreinit: fix Unix mmap failure detection and other robustness issues

- MemMapperUnix: mmap returns MAP_FAILED (not NULL) on failure; translate it to nullptr so the existing '!ptr' checks in the memory backend actually detect a failed reservation.

- coreinit: bound writes to the fixed 256-entry active-thread array.

- betype: operator|(betype) returned a reference to a local temporary; return by value like the sibling overload.

src/Cafe/OS/libs/coreinit/coreinit_Thread.cpp

@@ -154,8 +154,13 @@ namespace coreinit
 		}
 		if (alreadyActive == false)
 		{
-			activeThread[activeThreadCount] = threadMPTR;
-			activeThreadCount++;
+			if (activeThreadCount < 256)
+			{
+				activeThread[activeThreadCount] = threadMPTR;
+				activeThreadCount++;
+			}
+			else
+				cemuLog_log(LogType::Force, "coreinit: active thread list is full, cannot register thread");
 		}
 
 		__OSCreateHostThread(thread);

src/Common/betype.h

@@ -157,7 +157,7 @@ public:
 		return *this;
 	}
 
-	betype<T>& operator|(const betype<T>& v) const requires (requires (T& x, const T& y) { x | y; })
+	betype<T> operator|(const betype<T>& v) const requires (requires (T& x, const T& y) { x | y; })
 	{
 		betype<T> tmp(*this);
 		tmp.m_value = tmp.m_value | v.m_value;

src/util/MemMapper/MemMapperUnix.cpp

@@ -32,7 +32,8 @@ namespace MemMapper
 
 	void* ReserveMemory(void* baseAddr, size_t size, PAGE_PERMISSION permissionFlags)
 	{
-		return mmap(baseAddr, size, PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+		void* r = mmap(baseAddr, size, PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+		return r == MAP_FAILED ? nullptr : r;
 	}
 
 	void FreeReservation(void* baseAddr, size_t size)
@@ -55,7 +56,11 @@ namespace MemMapper
                 r = nullptr;
 		}
 		else
+		{
 			r = mmap(baseAddr, size, GetProt(permissionFlags), MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+			if (r == MAP_FAILED)
+				r = nullptr;
+		}
 		return r;
 	}