paste: fix warning on indentation in parallel()

_Bug_
Got the following error after cloning and running make:

paste.c: In function ‘parallel’:
paste.c:70:4: warning: this ‘else’ clause does not guard... [-Wmisleading-indentation]
    else
    ^~~~
paste.c:72:5: note: ...this statement, but the latter is misleadingly indented as if it is guarded by the ‘else’
     last++;
     ^~~~
This patch preserves the same functionality and just adjusts indentation to squelch the warning.

_Test plan_
Used the following 'script' to convince myself output looked correct for inputs
where the latter arguments to paste had fewer lines.

	make && printf "1\n2\n" > two.txt && printf "" > zero.txt && ./paste -d, two.txt zero.txt

paste.c

@@ -69,7 +69,7 @@ nextline:
 				putchar('\n');
 			else
 				efputrune(&d, stdout, "<stdout>");
-				last++;
+			last++;
 		}
 	}
 	if (last != -1)