fix(pdf): toolbar close label stays on one line in a narrow viewer

In a narrow PDF pane the toolbar has less room than its buttons need,
so they shrink to their min-content width. break-normal keeps an
English label like Close in one piece, but CJK text may break between
any two characters, so the Chinese, Japanese and Korean close labels
wrapped one character per line and stuck out of the toolbar.

Toolbar buttons are white-space: nowrap now.

src/main/frontend/extensions/pdf/pdf.css

@@ -77,7 +77,7 @@ input::-webkit-inner-spin-button {
       > .r {
         a.button {
           @apply select-none flex items-center mx-2 py-1 px-0.5 bg-transparent
-          transition-none break-normal hover:opacity-80;
+          transition-none break-normal whitespace-nowrap hover:opacity-80;
 
           &.is-active {
             @apply opacity-100 rounded-none;