TeX reader: fix parsing bug with comment at beginning of braced.

Closes #258.

Author: jgm

src/Text/TeXMath/Readers/TeX.hs

@@ -359,7 +359,7 @@ many1Exp :: TP Exp -> TP Exp
 many1Exp = manyExp' True
 
 inbraces :: TP Exp
-inbraces = braces (manyExp expr)
+inbraces = braces (ignorable *> manyExp expr)
 
 texToken :: TP Exp
 texToken = texSymbol <|> inbraces <|> texChar

test/regression/258.test

@@ -0,0 +1,13 @@
+<<< tex
+e^{
+ % below is the complex part:
+ \sum_i^n i^2 }
+>>> native
+[ ESuper
+    (EIdentifier "e")
+    (EGrouped
+       [ EUnderover
+           True (ESymbol Op "\8721") (EIdentifier "i") (EIdentifier "n")
+       , ESuper (EIdentifier "i") (ENumber "2")
+       ])
+]