Fix misleading indentation in stb_divide.h

[musicinmybrain]

With -Wmisleading-indentation (part of -Wall), gcc 11.2.1 warns:

  In file included from test_c_compilation.c:22:
  ../stb_divide.h: In function 'test':
  ../stb_divide.h:316:4: warning: this 'if' clause does not guard... [-Wmisleading-indentation]
    316 |    if (show) printf("(%+11d,%+2d)  ", q,r); stbdiv_check(q,r,a,b, "trunc",a);
        |    ^~
  ../stb_divide.h:316:45: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'if'
    316 |    if (show) printf("(%+11d,%+2d)  ", q,r); stbdiv_check(q,r,a,b, "trunc",a);
        |                                             ^~~~~~~~~~~~
  ../stb_divide.h:318:4: warning: this 'if' clause does not guard... [-Wmisleading-indentation]
    318 |    if (show) printf("(%+11d,%+2d)  ", q,r); stbdiv_check(q,r,a,b, "floor",b);
        |    ^~
  ../stb_divide.h:318:45: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'if'
    318 |    if (show) printf("(%+11d,%+2d)  ", q,r); stbdiv_check(q,r,a,b, "floor",b);
        |                                             ^~~~~~~~~~~~
  ../stb_divide.h:320:4: warning: this 'if' clause does not guard... [-Wmisleading-indentation]
    320 |    if (show) printf("(%+11d,%+2d)\n", q,r); stbdiv_check(q,r,a,b, "euclidean",1);
        |    ^~
  ../stb_divide.h:320:45: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'if'
    320 |    if (show) printf("(%+11d,%+2d)\n", q,r); stbdiv_check(q,r,a,b, "euclidean",1);
        |                                             ^~~~~~~~~~~~

This commit moves each call to stbdiv_check(…) to the following line to make clear that it is unconditional and to resolve the warning.

(This is a trivial fix; no need to add me to the list of contributors.)