patch 8.2.1493: not enough test coverage for the spell file handling

Problem:    Not enough test coverage for the spell file handling.
Solution:   Add spell file tests. (Yegappan Lakshmanan, closes #6728)

Author: brammool

src/spellfile.c

@@ -519,7 +519,7 @@ spell_load_file(
 		lp->sl_syllable = read_string(fd, len);	// <syllable>
 		if (lp->sl_syllable == NULL)
 		    goto endFAIL;
-		if (init_syl_tab(lp) == FAIL)
+		if (init_syl_tab(lp) != OK)
 		    goto endFAIL;
 		break;