Fix GH-18897: printf: empty precision is interpreted as precision 6, not as precision 0

Like in other languages, and especially C where printf originates from,
a missing precision should be treated as a 0 precision.
Because the ADJ_PRECISION flag was not set, the double formatting code
resetted the precision to the default float precision of 6.

Author: ndossche

ext/standard/formatted_print.c

@@ -591,6 +591,7 @@ php_formatted_print(char *format, size_t format_len, zval *args, int argc, int n
 						expprec = 1;
 					} else {
 						precision = 0;
+						adjusting |= ADJ_PRECISION;
 					}
 				} else {
 					precision = 0;

ext/standard/tests/strings/gh18897.phpt

@@ -0,0 +1,10 @@
+--TEST--
+GH-18897 (printf: empty precision is interpreted as precision 6, not as precision 0)
+--FILE--
+<?php
+printf("%.f\n", 3.1415926535);
+printf("%.0f\n", 3.1415926535);
+?>
+--EXPECT--
+3
+3