Fix a potential buffer overflow

When compiling with -Wformat-overflow=2 GCC reports:
  note: 'sprintf' output between 16 and 35 bytes into a destination of size 32

buffer.c

@@ -239,7 +239,7 @@ writeBufferName(Buffer *buf, int n)
 void
 gotoLine(Buffer *buf, int n)
 {
-    char msg[32];
+    char msg[36];
     Line *l = buf->firstLine;
 
     if (l == NULL)
@@ -284,7 +284,7 @@ gotoLine(Buffer *buf, int n)
 void
 gotoRealLine(Buffer *buf, int n)
 {
-    char msg[32];
+    char msg[36];
     Line *l = buf->firstLine;
 
     if (l == NULL)