Add some sanity checks guided by Android crash reports

Common/Thread/Promise.h

@@ -164,9 +164,11 @@ public:
 	void Cancel() {
 		std::lock_guard<std::mutex> guard(readyMutex_);
 		if (!ready_) {
-			_dbg_assert_(task_);
 			ready_ = true;
-			task_->Cancel();
+			_dbg_assert_(task_);
+			if (task_) {
+				task_->Cancel();
+			}
 			rx_->Release();
 			rx_ = nullptr;
 		}

Core/FileLoaders/ZipFileLoader.cpp

@@ -10,7 +10,7 @@
 ZipFileLoader::ZipFileLoader(FileLoader *sourceLoader)
 	: ProxiedFileLoader(sourceLoader), zipArchive_(nullptr) {
 	if (!backend_ || !backend_->Exists() || backend_->IsDirectory()) {
-		// bad
+		return;
 	}
 
 	zip_error_t error{};

Core/HLE/sceKernelModule.cpp

@@ -1323,10 +1323,10 @@ static PSPModule *__KernelLoadELFFromPtr(const u8 *ptr, size_t elfSize, u32 load
 		bool insertSymbols = scan && !reader.LoadSymbols();
 		std::vector<SectionID> codeSections = reader.GetCodeSections();
 		for (SectionID id : codeSections) {
-			u32 start = reader.GetSectionAddr(id);
+			const u32 start = reader.GetSectionAddr(id);
 			// Note: scan end is inclusive.
-			u32 end = start + reader.GetSectionSize(id) - 4;
-			u32 len = end + 4 - start;
+			const u32 end = start + reader.GetSectionSize(id) - 4;
+			const u32 len = end + 4 - start;
 			if (len == 0) {
 				// Seen in WWE: Smackdown vs Raw 2009. See #17435.
 				continue;

Core/MIPS/MIPSAnalyst.cpp

@@ -1023,7 +1023,7 @@ skip:
 	}
 
 	bool ScanForFunctions(u32 startAddr, u32 endAddr, bool insertSymbols) {
-		_assert_(((startAddr | endAddr) & 3) == 0);
+		_assert_((startAddr & 3) == 0);
 
 		std::lock_guard<std::recursive_mutex> guard(functions_lock);
 

GPU/Common/DrawEngineCommon.h

@@ -111,7 +111,7 @@ public:
 	}
 
 	void FlushSkin() {
-		if (dec_->skinInDecode) {
+		if (dec_ && dec_->skinInDecode) {
 			FlushPartialDecode();
 		}
 	}

GPU/Software/SoftGpu.cpp

@@ -661,7 +661,7 @@ void SoftGPU::BeginHostFrame() {
 }
 
 bool SoftGPU::PresentedThisFrame() const {
-	return presentation_->PresentedThisFrame();
+	return presentation_ ? presentation_->PresentedThisFrame() : false;
 }
 
 void SoftGPU::MarkDirty(uint32_t addr, uint32_t stride, uint32_t height, GEBufferFormat fmt, SoftGPUVRAMDirty value) {