[vala/0.40] vala: Don't use possibly uninitialized backing field of package_name

[Rico Tzschichholz <ricotz src gnome org>]

commit 9c3528c1bfd9ded40a1cce87016820170cd8d303
Author: Princeton Ferro <princetonferro gmail com>
Date:   Sat Apr 11 03:32:54 2020 -0400

    vala: Don't use possibly uninitialized backing field of package_name
    
    Don't check _package_name directly, which may be null at the time
    installed_version is accessed. This fixes a bug where Vala wouldn't
    generate errors when using symbols that are unavailable for a package
    version.
    
    Introduced by 7f0e90a5c34f437b7ab8f9197a9d42fc835b1a60
    
    Fixes https://gitlab.gnome.org/GNOME/vala/issues/971

 vala/valasourcefile.vala | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/vala/valasourcefile.vala b/vala/valasourcefile.vala
index 1263bcd7d..db605db20 100644
--- a/vala/valasourcefile.vala
+++ b/vala/valasourcefile.vala
@@ -70,7 +70,7 @@ public class Vala.SourceFile {
 
                        _version_requested = true;
 
-                       if (_package_name != null) {
+                       if (package_name != null) {
                                _installed_version = context.pkg_config_modversion (package_name);
                        }