ecpg: Fix error handling on OOMs when parsing timestamps

pgtypes_alloc() can return NULL when failing an allocation, which is
something that PGTYPEStimestamp_defmt_asc() has forgotten about when
translating a timestamp for 'D', 'r', 'R' and 'T' as these require a
temporary allocation.

This is unlikely going to be a problem in practice, so no backpatch is
done.

Author: Oleg Tselebrovskiy
Discussion: https://postgr.es/m/bf47888585149f83b276861a1662f7e4@postgrespro.ru

Author: michaelpq

src/interfaces/ecpg/pgtypeslib/dt_common.c

@@ -2659,6 +2659,8 @@ PGTYPEStimestamp_defmt_scan(char **str, char *fmt, timestamp * d,
 				 */
 				pfmt++;
 				tmp = pgtypes_alloc(strlen("%m/%d/%y") + strlen(pstr) + 1);
+				if (!tmp)
+					return 1;
 				strcpy(tmp, "%m/%d/%y");
 				strcat(tmp, pfmt);
 				err = PGTYPEStimestamp_defmt_scan(&pstr, tmp, d, year, month, day, hour, minute, second, tz);
@@ -2784,6 +2786,8 @@ PGTYPEStimestamp_defmt_scan(char **str, char *fmt, timestamp * d,
 			case 'r':
 				pfmt++;
 				tmp = pgtypes_alloc(strlen("%I:%M:%S %p") + strlen(pstr) + 1);
+				if (!tmp)
+					return 1;
 				strcpy(tmp, "%I:%M:%S %p");
 				strcat(tmp, pfmt);
 				err = PGTYPEStimestamp_defmt_scan(&pstr, tmp, d, year, month, day, hour, minute, second, tz);
@@ -2792,6 +2796,8 @@ PGTYPEStimestamp_defmt_scan(char **str, char *fmt, timestamp * d,
 			case 'R':
 				pfmt++;
 				tmp = pgtypes_alloc(strlen("%H:%M") + strlen(pstr) + 1);
+				if (!tmp)
+					return 1;
 				strcpy(tmp, "%H:%M");
 				strcat(tmp, pfmt);
 				err = PGTYPEStimestamp_defmt_scan(&pstr, tmp, d, year, month, day, hour, minute, second, tz);
@@ -2837,6 +2843,8 @@ PGTYPEStimestamp_defmt_scan(char **str, char *fmt, timestamp * d,
 			case 'T':
 				pfmt++;
 				tmp = pgtypes_alloc(strlen("%H:%M:%S") + strlen(pstr) + 1);
+				if (!tmp)
+					return 1;
 				strcpy(tmp, "%H:%M:%S");
 				strcat(tmp, pfmt);
 				err = PGTYPEStimestamp_defmt_scan(&pstr, tmp, d, year, month, day, hour, minute, second, tz);