Fix a bug in slice global inits where guard expressions were disregarded

Author: danpoe

regression/goto-instrument/slice-global-inits2/main.c

@@ -0,0 +1,12 @@
+
+int x;
+int y;
+
+int main()
+{
+  if (x) {
+    y = 1;
+  }
+
+  return 0;
+}

regression/goto-instrument/slice-global-inits2/test.desc

@@ -0,0 +1,9 @@
+CORE
+main.c
+--slice-global-inits
+x = 0;$
+y = 0;$
+^EXIT=0$
+^SIGNAL=0$
+--
+^warning: ignoring

regression/goto-instrument/slice-global-inits3/main.c

@@ -0,0 +1,12 @@
+
+int x;
+int y;
+
+void func(int a, int b) {}
+
+int main()
+{
+  func(x, y);
+
+  return 0;
+}

regression/goto-instrument/slice-global-inits3/test.desc

@@ -0,0 +1,9 @@
+CORE
+main.c
+--slice-global-inits
+x = 0;$
+y = 0;$
+^EXIT=0$
+^SIGNAL=0$
+--
+^warning: ignoring

src/goto-programs/slice_global_inits.cpp

@@ -77,6 +77,8 @@ void slice_global_inits(goto_modelt &goto_model)
     {
       const codet &code=i_it->code;
       code.visit(visitor);
+      const exprt &expr=i_it->guard;
+      expr.visit(visitor);
     }
   }