fix: Fix an issue where the module would attempt to generate og:locale tags without required ISO code

In the case where SEO features were enabled but the locales option did not contain required iso key,
the module would still attempt to generate those tags and thus crash the app, this adds a check on
ISO codes to prevent this error

Fixes #80

Author: paulgv

src/plugins/seo.js

@@ -39,18 +39,28 @@ Vue.mixin({
     .filter(item => !!item)
 
     // og:locale meta
-    const meta = [
-      // Replace dash with underscore as defined in spec: language_TERRITORY
-      { hid: 'og:locale', name: 'og:locale', property: 'og:locale', content: currentLocaleData[LOCALE_ISO_KEY].replace(/-/g, '_') },
+    const meta = []
+    // og:locale - current
+    if (currentLocaleData && currentLocaleData[LOCALE_ISO_KEY]) {
+      meta.push({
+        hid: 'og:locale',
+        name: 'og:locale',
+        property: 'og:locale',
+        // Replace dash with underscore as defined in spec: language_TERRITORY
+        content: currentLocaleData[LOCALE_ISO_KEY].replace(/-/g, '_')
+      })
+    }
+    // og:locale - alternate
+    meta.push(
       ...this.$i18n.locales
-        .filter(l => l[LOCALE_ISO_KEY] !== currentLocaleData[LOCALE_ISO_KEY])
+        .filter(l => l[LOCALE_ISO_KEY] && l[LOCALE_ISO_KEY] !== currentLocaleData[LOCALE_ISO_KEY])
         .map(locale => ({
           hid: 'og:locale:alternate-' + locale[LOCALE_ISO_KEY],
           name: 'og:locale:alternate',
           property: 'og:locale:alternate',
           content: locale[LOCALE_ISO_KEY].replace(/-/g, '_')
         }))
-    ]
+    );
 
     return {
       htmlAttrs,