fix px4_getopt: add argc check for options that take an argument

Fixes the following corner case:
mpu9250 start -R
This would return a valid result (myoptind < argc), but myoptind pointed
to a NULL argument (and thus mpu9250 would crash).
With this patch, px4_getopt will return '?', indicating a parser error.

src/platforms/common/px4_getopt.c

@@ -82,6 +82,10 @@ static int reorder(int argc, char **argv, const char *options)
 			tmpidx++;
 
 			if (takesarg) {
+				if (idx + 1 >= argc) { //Error: option takes an argument, but there is no more argument
+					return 1;
+				}
+
 				tmp_argv[tmpidx] = argv[idx + 1];
 				// printf("tmp_argv[%d] = %s\n", tmpidx, tmp_argv[tmpidx]);
 				tmpidx++;