mp_fdjac2: drop asserts made redundant by isfinite guard

bl4ckb0ne noted on PR collabora#364 that once the isfinite() sanitize-to-zero
guard runs, the following assert(isfinite(fjac[ij])) can never fire
in a debug build and is already a no-op under -DNDEBUG. Removed both
now-dead asserts (one-sided non-debug and debug paths).

Claude Code assisted with this change.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: rocketmark

redist/mpfit/mpfit.c

@@ -1231,7 +1231,6 @@ static int mp_fdjac2(mp_func funct, int m, int n, int *ifree, int npar, FLT *x,
 						/* assert is compiled out under NDEBUG; guard for real. */
 						if (!isfinite(fjac[ij]))
 							fjac[ij] = 0;
-						assert(isfinite(fjac[ij]));
 					}
 				} else {
 					/* Debug path for correctness */
@@ -1240,7 +1239,6 @@ static int mp_fdjac2(mp_func funct, int m, int n, int *ifree, int npar, FLT *x,
 						fjac[ij] = (wa[i] - fvec[i]) / h; /* fjac[i+m*j] */
 						if (!isfinite(fjac[ij]))
 							fjac[ij] = 0;
-						assert(isfinite(fjac[ij]));
 						if ((da == 0 && dr == 0 && (fjold != 0 || fjac[ij] != 0)) ||
 							((da != 0 || dr != 0) && (fabs(fjold - fjac[ij]) > da + fabs(fjold) * dr))) {
 							fprintf(stderr, "   %10d %10.4g %10.4g %10.4g %10.4g %10.4g\n", i, fvec[i], fjold, fjac[ij],