use AppContext.BaseDirectory when entry assembly location is empty

Author: honfika

src/Titanium.Web.Proxy/Certificates/Cache/DefaultCertificateDiskCache.cs

@@ -129,6 +129,12 @@ private string getRootCertificateDirectory()
                         assemblyLocation = Assembly.GetEntryAssembly().Location;
                     }
 
+                    // single-file app string.Empty location
+                    if (assemblyLocation == string.Empty)
+                    {
+                        assemblyLocation = AppContext.BaseDirectory;
+                    }
+
                     string path = Path.GetDirectoryName(assemblyLocation);
 
                     rootCertificatePath = path ?? throw new NullReferenceException();