fix: maybeSingle: Avoid uncaught promise rejection (#210)

Not all errors returned by postgrest contain the `details` field (in
particular, 401 errors due to invalid/expired JWT tokens). Hence, this
PR avoids an uncaught promise rejection by ensuring that `error.details`
field exists before checking the error details for the "Results contain
0 rows" message.

Author: bnjmnt4n

src/lib/PostgrestTransformBuilder.ts

@@ -104,7 +104,7 @@ export default class PostgrestTransformBuilder<T> extends PostgrestBuilder<T> {
     const _this = new PostgrestTransformBuilder(this)
     _this.then = ((onfulfilled: any, onrejected: any) =>
       this.then((res: any): any => {
-        if (res.error?.details.includes('Results contain 0 rows')) {
+        if (res.error?.details?.includes('Results contain 0 rows')) {
           return onfulfilled({
             error: null,
             data: null,