[scudo] Don't unmap other low memory pages if mapping doesn't exist

[ddcc]

Summary

Tests can register multiple allocators, but only the first will initialize since it initializes the TSDRegistrySharedT. Then, destruction of subsequent allocator may end up unmapping a nullptr PrimaryBase with non-zero PrimarySize.

[vitalybuka]

compiler-rt/lib/scudo/standalone/primary64.h

93

please clangformat

compiler-rt/lib/scudo/standalone/primary64.h

void init(s32 ReleaseToOsInterval) {
     setOption(Option::ReleaseInterval, static_cast<sptr>(ReleaseToOsInterval));
   }
 
   void unmapTestOnly() {
     for (uptr I = 0; I < NumClasses; I++) {
       RegionInfo *Region = getRegionInfo(I);
       *Region = {};
     }
-    unmap(reinterpret_cast<void *>(PrimaryBase), PrimarySize, UNMAP_ALL, &Data);
+    if (PrimaryBase)
+      unmap(reinterpret_cast<void *>(PrimaryBase), PrimarySize, UNMAP_ALL,
+            &Data);
     PrimaryBase = 0U;
   }
 
   TransferBatch *popBatch(CacheT *C, uptr ClassId) {
     DCHECK_LT(ClassId, NumClasses);
     RegionInfo *Region = getRegionInfo(ClassId);
     ScopedLock L(Region->Mutex);
     TransferBatch *B = Region->FreeList.front();