patch 8.2.2948: substitute() accepts a number but not a float expression

Problem:    Substitute() accepts a number but not a float expression.
Solution:   Also accept a float. (closes #8331)
diff --git a/src/typval.c b/src/typval.c
index f08d1aa..a17dbef 100644
--- a/src/typval.c
+++ b/src/typval.c
@@ -462,8 +462,13 @@
 	    break;
 	case VAR_FLOAT:
 #ifdef FEAT_FLOAT
-	    emsg(_(e_float_as_string));
-	    break;
+	    if (strict)
+	    {
+		emsg(_(e_float_as_string));
+		break;
+	    }
+	    vim_snprintf((char *)buf, NUMBUFLEN, "%g", varp->vval.v_float);
+	    return buf;
 #endif
 	case VAR_STRING:
 	    if (varp->vval.v_string != NULL)