TextureCache: Warn for invalid custom textures

At the moment, custom textures with:
- invalid mipmap size
- invalid aspect ratio
- non-fractional scaling factors
are allowed. But they can't be loaded fine by the backend, so generate a warning if someone trys to load them.

Source/Core/VideoCommon/TextureCacheBase.cpp

@@ -255,11 +255,12 @@ PC_TexFormat TextureCache::LoadCustomTexture(u64 tex_hash, int texformat, unsign
 	char texPathTemp[MAX_PATH];
 	unsigned int newWidth = 0;
 	unsigned int newHeight = 0;
+	u32 tex_hash_u32 = tex_hash & 0x00000000FFFFFFFFLL;
 
 	if (level == 0)
-		sprintf(texPathTemp, "%s_%08x_%i", SConfig::GetInstance().m_LocalCoreStartupParameter.m_strUniqueID.c_str(), (u32) (tex_hash & 0x00000000FFFFFFFFLL), texformat);
+		sprintf(texPathTemp, "%s_%08x_%i", SConfig::GetInstance().m_LocalCoreStartupParameter.m_strUniqueID.c_str(), tex_hash_u32, texformat);
 	else
-		sprintf(texPathTemp, "%s_%08x_%i_mip%i", SConfig::GetInstance().m_LocalCoreStartupParameter.m_strUniqueID.c_str(), (u32) (tex_hash & 0x00000000FFFFFFFFLL), texformat, level);
+		sprintf(texPathTemp, "%s_%08x_%i_mip%i", SConfig::GetInstance().m_LocalCoreStartupParameter.m_strUniqueID.c_str(), tex_hash_u32, texformat, level);
 
 	unsigned int required_size = 0;
 	PC_TexFormat ret = HiresTextures::GetHiresTex(texPathTemp, &newWidth, &newHeight, &required_size, texformat, temp_size, temp);
@@ -275,6 +276,13 @@ PC_TexFormat TextureCache::LoadCustomTexture(u64 tex_hash, int texformat, unsign
 
 	if (ret != PC_TEX_FMT_NONE)
 	{
+		if (level > 0 && (newWidth != width || newHeight != height))
+			ERROR_LOG(VIDEO, "Invalid custom texture size %dx%d for texture %s. This mipmap layer _must_ be %dx%d.", newWidth, newHeight, texPathTemp, width, height);
+		if (newWidth * height != newHeight * width)
+			ERROR_LOG(VIDEO, "Invalid custom texture size %dx%d for texture %s. The aspect differs from the native size %dx%d.", newWidth, newHeight, texPathTemp, width, height);
+		if (newWidth % width || newHeight % height)
+			WARN_LOG(VIDEO, "Invalid custom texture size %dx%d for texture %s. Please use an integer upscaling factor based on the native size %dx%d.", newWidth, newHeight, texPathTemp, width, height);
+
 		width = newWidth;
 		height = newHeight;
 	}