Initialize GraphicsMagick on library load

GNU Data Language library uses GraphicsMagick via static variables as well.
These get initialized and used on its library load and initialization. For
this reason GM library needs to be initialized on GDL library load.

Closes: #927307

src/magick_cl.cpp

@@ -66,6 +66,10 @@ namespace lib {
   unsigned int gCount = 0;
   static bool notInitialized = true;
 
+  __attribute__((constructor)) static void init(void) {
+    START_MAGICK;
+  }
+
   void magick_setup() {
     int i;
     for (i = 0; i < 40; ++i) gValid[i] = 0;