Common: Correctly set ptr to null if mmap fails in memory_util

On POSIX systems mmap will return MAP_FAILED ((void*)-1) instead of a null pointer.

src/common/memory_util.cpp

@@ -51,13 +51,13 @@ void* AllocateExecutableMemory(size_t size, bool low)
     // printf("Mapped executable memory at %p (size %ld)\n", ptr,
     //    (unsigned long)size);
     
-#if defined(__FreeBSD__)
-    if (ptr == MAP_FAILED)
+#ifdef _WIN32
+    if (ptr == nullptr)
     {
-        ptr = NULL;
 #else
-    if (ptr == NULL)
+    if (ptr == MAP_FAILED)
     {
+        ptr = nullptr;
 #endif 
         PanicAlert("Failed to allocate executable memory");
     }
@@ -88,6 +88,9 @@ void* AllocateMemoryPages(size_t size)
 #else
     void* ptr = mmap(0, size, PROT_READ | PROT_WRITE,
             MAP_ANON | MAP_PRIVATE, -1, 0);
+
+    if (ptr == MAP_FAILED)
+        ptr = nullptr;
 #endif
 
     // printf("Mapped memory at %p (size %ld)\n", ptr,