psql: Make ParseVariableDouble reject values above max

ParseVariableDouble missed returning false after logging an error when
the parsed value exceeded max, making the value assigned rather than
rejected.  Backpatch down to v18 where this was introduced as part of
the \WATCH_INTERVAL.

Author: Sven Klemm <sven@tigerdata.com>
Co-authored-by: Daniel Gustafsson <daniel@yesql.se>
Reviewed-by: Daniel Gustafsson <daniel@yesql.se>
Discussion: https://postgr.es/m/CAMCrgp31p_5SDVi7dwnP39tTW5icQ0MWHA+N4kJdXgkL0PEy8w@mail.gmail.com
Backpatch-through: 18

src/bin/psql/t/001_basic.pl

@@ -451,6 +451,8 @@ psql_fails_like(
 	'\set WATCH_INTERVAL 1e500',
 	qr/is out of range/,
 	'WATCH_INTERVAL variable is out of range');
+psql_like($node, '\echo :WATCH_INTERVAL',
+	qr/^2$/m, 'WATCH_INTERVAL variable was not altered');
 
 # Test \g output piped into a program.
 # The program is perl -pe '' to simply copy the input to the output.

src/bin/psql/variables.c

@@ -224,6 +224,7 @@ ParseVariableDouble(const char *value, const char *name, double *result, double
 			if (name)
 				pg_log_error("invalid value \"%s\" for variable \"%s\": must be less than %.2f",
 							 value, name, max);
+			return false;
 		}
 		*result = dblval;
 		return true;