fix(b-img-lazy): fix blank-src not work error (#6302)

use BImgLazy computed value props overwrite default BImg props

Co-authored-by: Jacob Müller <jacob.mueller.elz@gmail.com>

src/components/image/img-lazy.js

@@ -140,15 +140,15 @@ export const BImgLazy = /*#__PURE__*/ Vue.extend({
     return h(BImg, {
       directives,
       props: {
+        // Passthrough props
+        ...pluckProps(imgProps, this.$props),
         // Computed value props
         src: this.computedSrc,
         blank: this.computedBlank,
         width: this.computedWidth,
         height: this.computedHeight,
         srcset: this.computedSrcset || null,
-        sizes: this.computedSizes || null,
-        // Passthrough props
-        ...pluckProps(imgProps, this.$props)
+        sizes: this.computedSizes || null
       }
     })
   }