LaTeX reader: fix parsing of dimensions beginning with ..

E.g., `\kern.1pt`.

Closes #9902.

src/Text/Pandoc/Readers/LaTeX/Parsing.hs

@@ -885,7 +885,12 @@ dimenarg = try $ do
   optional sp
   ch  <- option False $ True <$ symbol '='
   minus <- option "" $ "-" <$ symbol '-'
-  Tok _ _ s1 <- satisfyTok isWordTok
+  s1 <- option ""
+        (do Tok _ _ s1 <- satisfyTok isWordTok
+            guard (case T.uncons s1 of
+                     Just (c,_) -> isDigit c
+                     Nothing -> False)
+            pure s1)
   s2 <- option "" $ try $ do
           symbol '.'
           Tok _ _ t <-  satisfyTok isWordTok

test/command/9902.md

@@ -0,0 +1,6 @@
+```
+% pandoc -t native -f latex+raw_tex
+\kern.1pt
+^D
+[ RawBlock (Format "latex") "\\kern.1pt" ]
+```