patch 8.2.2462: Coverity warns for not checking for fseek() error

Problem:    Coverity warns for not checking for fseek() error.
Solution:   Give an error message if fseek() fails.
diff --git a/src/spellfile.c b/src/spellfile.c
index 869db7f..2018169 100644
--- a/src/spellfile.c
+++ b/src/spellfile.c
@@ -6277,7 +6277,11 @@
 							 len, word, NameBuff);
 			}
 		    }
-		    fseek(fd, fpos_next, SEEK_SET);
+		    if (fseek(fd, fpos_next, SEEK_SET) != 0)
+		    {
+			PERROR(_("Seek error in spellfile"));
+			break;
+		    }
 		}
 	    }
 	    if (fd != NULL)