DataFlash: account for snprintf now null-terminating strings

libraries/DataFlash/DataFlash.cpp

@@ -431,7 +431,7 @@ bool DataFlash_Class::logging_failed() const
 
 void DataFlash_Class::Log_Write_MessageF(const char *fmt, ...)
 {
-    char msg[64] {};
+    char msg[65] {}; // sizeof(log_Message.msg) + null-termination
 
     va_list ap;
     va_start(ap, fmt);

libraries/DataFlash/DataFlash_Backend.cpp

@@ -408,7 +408,7 @@ bool DataFlash_Backend::ShouldLog(bool is_critical)
 
 bool DataFlash_Backend::Log_Write_MessageF(const char *fmt, ...)
 {
-    char msg[64] {};
+    char msg[65] {}; // sizeof(log_Message.msg) + null-termination
 
     va_list ap;
     va_start(ap, fmt);