use explicit 32bit integer for fractional time calculation

minmea.c

@@ -300,8 +300,8 @@ bool minmea_scan(const char *sentence, const char *format, ...)
 
                     // Extra: fractional time. Saved as microseconds.
                     if (*field++ == '.') {
-                        int value = 0;
-                        int scale = 1000000;
+                        uint32_t value = 0;
+                        uint32_t scale = 1000000LU;
                         while (isdigit((unsigned char) *field) && scale > 1) {
                             value = (value * 10) + (*field++ - '0');
                             scale /= 10;