correctly index if/elif/else statements

Summary:
the else branch isn't indexed in "if / elif / else" constructs. This fixes it.

Note: due the dynamic nature of python and absence of exhaustiveness check, it's difficult to cover all cases. Could be worth trying to being more defensive in the traversal

Differential Revision: D87634991

fbshipit-source-id: 7bf42c06a3dfb8c3ca9aed31c14d28b8f4285a16

Author: Philippe Bidinger

glean/glass/test/regression/tests/buck/documentSymbolIndex_my_defs.out

@@ -3,7 +3,7 @@
     {
         "referenced_file_digests": {},
         "revision": "testhash",
-        "size": 22,
+        "size": 23,
         "symbols": {
             "1": [
                 {
@@ -593,6 +593,41 @@
                     }
                 }
             ],
+            "38": [
+                {
+                    "attributes": {
+                        "symbolKind": {
+                            "aInteger": 3
+                        },
+                        "symbolLanguage": {
+                            "aInteger": 11
+                        },
+                        "symbolName": {
+                            "aString": "g"
+                        },
+                        "symbolParent": {
+                            "aString": "buck_project/my_defs.bzl"
+                        }
+                    },
+                    "range": {
+                        "columnBegin": 16,
+                        "columnEnd": 17,
+                        "lineBegin": 38,
+                        "lineEnd": 38
+                    },
+                    "sym": "test/buck/d/buck_project/my_defs.bzl/g",
+                    "target": {
+                        "filepath": "buck_project/my_defs.bzl",
+                        "range": {
+                            "columnBegin": 1,
+                            "columnEnd": 16,
+                            "lineBegin": 7,
+                            "lineEnd": 8
+                        },
+                        "repository": "test"
+                    }
+                }
+            ],
             "4": [
                 {
                     "attributes": {