[LyX/master] Amend 0dc7f34e: avoid using a C++20 function.

[Thibaut Cuvelier]

commit dec53304268388a46805418a5b531c2b48eb0f22
Author: Thibaut Cuvelier <tcuvelier at lyx.org>
Date:   Sun Feb 20 02:03:41 2022 +0100

    Amend 0dc7f34e: avoid using a C++20 function.
---
 src/Encoding.cpp |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/src/Encoding.cpp b/src/Encoding.cpp
index 4e47dae..988872f 100644
--- a/src/Encoding.cpp
+++ b/src/Encoding.cpp
@@ -727,7 +727,7 @@ void Encodings::read(FileName const & encfile, FileName const & symbolsfile)
 		symbol = tmp;
 
 		// Special case: more than one entry for one character (to add other LaTeX commands).
-		if (unicodesymbols.contains(symbol)) {
+		if (unicodesymbols.find(symbol) != unicodesymbols.end()) {
 			if (!symbolsLex.next(true))
 				break;
 			docstring textCommand = symbolsLex.getDocString();