EGL: fix an extension string bug

This change fixes a bug where initializing EGL multiple times (eglTerminate
followed by eglInitialize) would cause extensions to show up in the extension
string multiple times.

Change-Id: I707a3da62ed30ef13835087167f84a08bc6addd7

opengl/libs/EGL/egl_display.cpp

@@ -293,6 +293,10 @@ EGLBoolean egl_display_t::terminate() {
 
     mHibernation.setDisplayValid(false);
 
+    // Reset the extension string since it will be regenerated if we get
+    // reinitialized.
+    mExtensionString.setTo("");
+
     // Mark all objects remaining in the list as terminated, unless
     // there are no reference to them, it which case, we're free to
     // delete them.