Fix deletion of if (SEF_expr) ;

Fixes #29. Thanks @KrsityKu for the test case, which was added to the test suite.

unit_tests/regression.suite/issue-29.lsl

@@ -0,0 +1,12 @@
+default
+{
+    touch(integer num)
+    {
+        integer dead = 0;
+        if (num == 5)
+            dead = 1;
+        else
+            dead = 2;
+        llOwnerSay("Not Dead");
+    }
+}

unit_tests/regression.suite/issue-29.out

@@ -0,0 +1,7 @@
+default
+{
+    touch(integer num)
+    {
+        llOwnerSay("Not Dead");
+    }
+}