initialize two more struct Tree members to appease coverity scan

src/variable.h

@@ -88,17 +88,15 @@ class Variable : protected Pointers {
     int nvector;           // length of array for vector-style variable
     int nstride;           // stride between atoms if array is a 2d array
     int selfalloc;         // 1 if array is allocated here, else 0
-    int ivalue1,ivalue2;   // extra values for needed for gmask,rmask,grmask
+    int ivalue1,ivalue2;   // extra values needed for gmask,rmask,grmask
     int nextra;            // # of additional args beyond first 2
     Tree *first,*second;   // ptrs further down tree for first 2 args
     Tree **extra;          // ptrs further down tree for nextra args
 
     Tree() :
       array(NULL), iarray(NULL), barray(NULL),
-      selfalloc(0), nextra(0),
-      first(NULL), second(NULL), extra(NULL)
-    {
-    }
+      selfalloc(0), ivalue1(0), ivalue2(0), nextra(0),
+      first(NULL), second(NULL), extra(NULL) {}
   };
 
   int compute_python(int);