move sample loop fixup to dedicated function

in order to stay in sync with FluidSynth#184

fluidsynth/src/sfloader/fluid_defsfont.c

@@ -1959,23 +1959,7 @@ fluid_sample_import_sfont(fluid_sample_t* sample, SFSample* sfsample, fluid_defs
     sample->start = 0;
     sample->end = sfinfo.frames - 1;
 
-    /* loop is fowled?? (cluck cluck :) */
-    if (sample->loopend > sample->end ||
-        sample->loopstart >= sample->loopend ||
-        sample->loopstart <= sample->start)
-    {
-      /* can pad loop by 8 samples and ensure at least 4 for loop (2*8+4) */
-      if ((sample->end - sample->start) >= 20)
-      {
-        sample->loopstart = sample->start + 8;
-        sample->loopend = sample->end - 8;
-      }
-      else /* loop is fowled, sample is tiny (can't pad 8 samples) */
-      {
-        sample->loopstart = sample->start + 1;
-        sample->loopend = sample->end - 1;
-      }
-    }
+    fixup_sample_loop(sample);
 #endif
   }