CRT_degreeSign code shrink

Make "CRT_degreeSign" a writable buffer that will be updated after the
initDegreeSign() function. This avoids needing a static buffer in the
function.

Also use MB_LEN_MAX for the buffer size, which is more appropriate than
the magic number 4.

One side effect of this change is that "CRT_degreeSign" will lose the
const qualifier in the header (CRT.h).

Signed-off-by: Kang-Che Sung <explorer09@gmail.com>

Author: Explorer09

CRT.c

@@ -12,6 +12,7 @@ in the source distribution for its full text.
 #include <errno.h>
 #include <fcntl.h>
 #include <langinfo.h>
+#include <limits.h>
 #include <signal.h>
 #include <stdarg.h>
 #include <stdio.h>
@@ -94,21 +95,25 @@ const char* const* CRT_treeStr = CRT_treeStrAscii;
 
 static const Settings* CRT_settings;
 
-const char* CRT_degreeSign;
+#ifdef HAVE_LIBNCURSESW
+char CRT_degreeSign[MB_LEN_MAX] = "\xc2\xb0";
+#else
+char CRT_degreeSign[] = "";
+#endif
 
-static const char* initDegreeSign(void) {
+static void initDegreeSign(void) {
 #ifdef HAVE_LIBNCURSESW
    if (CRT_utf8)
-      return "\xc2\xb0";
+      return;
 
-   static char buffer[4];
    // this might fail if the current locale does not support wide characters
-   int r = snprintf(buffer, sizeof(buffer), "%lc", 176);
-   if (r > 0)
-      return buffer;
+   int r = snprintf(CRT_degreeSign, sizeof(CRT_degreeSign), "%lc", 176);
+   if (r <= 0)
+      CRT_degreeSign[0] = '\0';
 #endif
 
-   return "";
+   // No-op
+   return;
 }
 
 const int* CRT_colors;
@@ -1145,7 +1150,7 @@ IGNORE_WCASTQUAL_END
 
    CRT_setMouse(settings->enableMouse);
 
-   CRT_degreeSign = initDegreeSign();
+   initDegreeSign();
 }
 
 void CRT_done(void) {

CRT.h

@@ -176,7 +176,7 @@ void CRT_handleSIGSEGV(int signal) ATTR_NORETURN;
 #define KEY_FOCUS_IN  (KEY_MAX + 'I')
 #define KEY_FOCUS_OUT (KEY_MAX + 'O')
 
-extern const char* CRT_degreeSign;
+extern char CRT_degreeSign[];
 
 #ifdef HAVE_LIBNCURSESW