Add braces for if block with large comment in psql's common.c

A patch touching this area of the code is under review, and this format
makes the readability of the code slightly harder to parse.

Extracted from a larger patch by the same author.

Author: Anthonin Bonnefoy <anthonin.bonnefoy@datadoghq.com>
Discussion: https://postgr.es/m/CAO6_XqroE7JuMEm1sWz55rp9fAYX2JwmcP_3m_v51vnOFdsLiQ@mail.gmail.com

src/bin/psql/common.c

@@ -1577,7 +1577,7 @@ ExecQueryAndProcessResults(const char *query,
 			if (result_status == PGRES_COPY_BOTH ||
 				result_status == PGRES_COPY_OUT ||
 				result_status == PGRES_COPY_IN)
-
+			{
 				/*
 				 * For some obscure reason PQgetResult does *not* return a
 				 * NULL in copy cases despite the result having been cleared,
@@ -1585,6 +1585,7 @@ ExecQueryAndProcessResults(const char *query,
 				 * ignore manually.
 				 */
 				result = NULL;
+			}
 			else
 				result = PQgetResult(pset.db);