[common.iter.nav] Avoid newline in index entry

Fixes #4544

Author: jwakely

source/iterators.tex

@@ -5004,7 +5004,7 @@
 Otherwise, if
 \tcode{requires (I\& i) \{ \{ *i++ \} -> \exposconceptnc{can-reference}; \}}
 is \tcode{true} or
-\tcode{\libconcept{constructible_\newline{}from}<iter_value_t<I>, iter_reference_t<I>>}
+\tcode{\libconceptx{constructible_\newline{}from}{constructible_from}<iter_value_t<I>, iter_reference_t<I>>}
 is \tcode{false},
 equivalent to:
 \begin{codeblock}