renderer_vulkan: Misc fixes (#6974)

* vk_platform: Check if library was loaded

* pica_to_vk: Dont crash on unknow blend equation

src/common/dynamic_library/dynamic_library.h

@@ -16,7 +16,7 @@ public:
     ~DynamicLibrary();
 
     /// Returns true if the library is loaded, otherwise false.
-    [[nodiscard]] bool IsLoaded() {
+    [[nodiscard]] bool IsLoaded() const noexcept {
         return handle != nullptr;
     }