fix: pass unsigned chars to the cctype functions

Differently from their <locale> counterparts, the functions in <cctype>
and <ctype.h> have undefined behavior if their argument is not
representable as an unsigned char and is not equal to EOF.

Author: gennaroprota

src/lib/AST/ParseJavadoc.cpp

@@ -7,6 +7,7 @@
 // Copyright (c) 2023 Vinnie Falco ([email protected])
 // Copyright (c) 2023 Krystian Stasiowski ([email protected])
 // Copyright (c) 2024 Alan de Freitas ([email protected])
+// Copyright (c) 2025 Gennaro Prota ([email protected])
 //
 // Official repository: https://github.com/cppalliance/mrdocs
 //
@@ -540,7 +541,7 @@ parseStyled(StringRef s)
         }
     };
 
-    auto isPunctuationOrSpace = [](char c) {
+    auto isPunctuationOrSpace = [](unsigned char c) {
         return std::isspace(c) || std::ispunct(c);
     };
 

src/lib/Support/Validate.cpp

@@ -4,6 +4,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 // Copyright (c) 2023 Vinnie Falco ([email protected])
+// Copyright (c) 2025 Gennaro Prota ([email protected])
 //
 // Official repository: https://github.com/cppalliance/mrdocs
 //
@@ -29,7 +30,7 @@ validAdocSectionID(
     return
         s[0] == '_' ||
         s[0] == ':' ||
-        std::isalpha(s[0]);
+        std::isalpha(static_cast<unsigned char>(s[0]));
 }
 
 } // mrdocs