gst-plugins-base,gst_all_1.gst-plugins-base: apply patch for CVE-2019-9928

Refactor the patchPhase management for the package along the way to
something more standard.

(Cherry pick from 97e4a11b003a5a88397d9a1fc4ee8ce8f006a396 with an extra
version of the package to patch in 19.03.)

pkgs/development/libraries/gstreamer/base/default.nix

···
         sha256 = "07x43xis0sr0hfchf36ap0cibx0lkfpqyszb3r3w9dzz301fk04z";
     })
     ./fix_pkgconfig_includedir.patch
+    (fetchurl {
+      url = "https://gitlab.freedesktop.org/gstreamer/gst-plugins-base/commit/f672277509705c4034bc92a141eefee4524d15aa.patch";
+      name = "CVE-2019-9928.patch";
+      sha256 = "0hz3lsq3ppmaf329sbyi05y1qniqfj9vlp2f3z918383pvrcms4i";
+    })
   ];
 }

pkgs/development/libraries/gstreamer/legacy/gst-plugins-base/default.nix

···
     sha256 = "0jp6hjlra98cnkal4n6bdmr577q8mcyp3c08s3a02c4hjhw5rr0z";
   };
 
-  patchPhase = ''
+  patches = [
+    ./gcc-4.9.patch
+    (fetchurl {
+      url = "https://gitlab.freedesktop.org/gstreamer/gst-plugins-base/commit/f672277509705c4034bc92a141eefee4524d15aa.patch";
+      name = "CVE-2019-9928.patch";
+      sha256 = "0hz3lsq3ppmaf329sbyi05y1qniqfj9vlp2f3z918383pvrcms4i";
+    })
+  ];
+
+  postPatch = ''
     sed -i 's@/bin/echo@echo@g' configure
     sed -i -e 's/^   /\t/' docs/{libs,plugins}/Makefile.in
-
-    patch -p1 < ${./gcc-4.9.patch}
   '';
 
   outputs = [ "out" "dev" ];