Fix various clang warnings.

Fix various clang warnings.

../show.c:668:30: warning: variable 'q' is uninitialized when used here [-Wuninitialized]
                                        s = sr_period_string(p, q);
                                                                ^
../show.c:324:30: note: initialize the variable 'q' to silence this warning
        const uint64_t *uint64, p, q, low, high;
                                    ^
                                     = 0
../show.c:668:27: warning: variable 'p' is uninitialized when used here [-Wuninitialized]
                                        s = sr_period_string(p, q);
                                                             ^
../show.c:324:27: note: initialize the variable 'p' to silence this warning
        const uint64_t *uint64, p, q, low, high;
                                 ^
                                  = 0
../show.c:458:58: warning: variable 'high' is uninitialized when used here [-Wuninitialized]
                                printf("    Maximum number of samples: %"PRIu64"\n", high);
                                                                                     ^~~~
../show.c:324:41:   CC       input.o
note: initialize the variable 'high' to silence this warning
        const uint64_t *uint64, p, q, low, high;
                                               ^
                                                = 0
../show.c:589:33: warning: variable 'low' is uninitialized when used here [-Wuninitialized]
                                printf("%"PRIu64"-%"PRIu64, low, high);
                                                            ^~~
../show.c:324:35: note: initialize the variable 'low' to silence this warning
        const uint64_t *uint64, p, q, low, high;
                                         ^
                                          = 0