loader; Resolve sign conversion/truncation errors

src/core/file_sys/kernel_executable.cpp

@@ -147,7 +147,7 @@ std::vector<u32> KIP::GetKernelCapabilities() const {
 }
 
 s32 KIP::GetMainThreadPriority() const {
-    return header.main_thread_priority;
+    return static_cast<s32>(header.main_thread_priority);
 }
 
 u32 KIP::GetMainThreadStackSize() const {