enigma: fix build

srcpkgs/enigma/patches/fix-ifstream_test.patch

@@ -0,0 +1,11 @@
+--- src/lev/Proxy.cc	2014-12-19 22:24:37.000000000 +0100
++++ src/lev/Proxy.cc	2017-09-01 16:55:50.009413332 +0200
+@@ -933,7 +933,7 @@
+                     } else if (haveLocalCopy) {
+                         // plain file
+                         basic_ifstream<char> ifs(absExtPath.c_str(), ios::binary | ios::in);
+-                        if (ifs != NULL)
++                        if (ifs)
+                             Readfile(ifs, extCode);
+                         else
+                             haveLocalCopy = false;