Fixed small distance replies on GEODIST and GEO commands WITHDIST (#11631)

Fixes a regression introduced by #11552 in 7.0.6.
it causes replies in the GEO commands to contain garbage when the
result is a very small distance (less than 1)
Includes test to confirm indeed with junk in buffer now we properly reply

(cherry picked from commit d7b4c9175e)

src/util.c

@@ -643,9 +643,7 @@ int fixedpoint_d2string(char *dst, size_t dstlen, double dvalue, int fractional_
     if (dvalue == 0) {
         dst[0] = '0';
         dst[1] = '.';
-        for (int i = 0; i < fractional_digits; i++) {
-            dst[2 + i] = '0';
-        }
+        memset(dst + 2, '0', fractional_digits);
         dst[fractional_digits+2] = '\0';
         return fractional_digits + 2;
     }
@@ -694,10 +692,8 @@ int fixedpoint_d2string(char *dst, size_t dstlen, double dvalue, int fractional_
     }
     dst[integer_digits] = '.';
     int size = integer_digits + 1 + fractional_digits;
-    /* fill with 0 if required until fractional_digits */
-    for (int i = integer_digits + 1; i < fractional_digits; i++) {
-        dst[i] = '0';
-    }
+    /* fill with 0 from fractional digits until size */
+    memset(dst + integer_digits + 1, '0', fractional_digits);
     int next = size - 1;
     while (value >= 100) {
         int const i = (value % 100) * 2;
@@ -1246,6 +1242,20 @@ static void test_fixedpoint_d2string(void) {
     sz = fixedpoint_d2string(buf, sizeof buf, v, 1);
     assert(sz == 3);
     assert(!strcmp(buf, "0.0"));
+    /* set junk in buffer */
+    memset(buf,'A',32);
+    v = 0.0001;
+    sz = fixedpoint_d2string(buf, sizeof buf, v, 4);
+    assert(sz == 6);
+    assert(buf[sz] == '\0');
+    assert(!strcmp(buf, "0.0001"));
+    /* set junk in buffer */
+    memset(buf,'A',32);
+    v = 6.0642951598391699e-05;
+    sz = fixedpoint_d2string(buf, sizeof buf, v, 4);
+    assert(sz == 6);
+    assert(buf[sz] == '\0');
+    assert(!strcmp(buf, "0.0001"));
     v = 0.01;
     sz = fixedpoint_d2string(buf, sizeof buf, v, 4);
     assert(sz == 6);

tests/unit/geo.tcl

@@ -502,6 +502,13 @@ start_server {tags {"geo"}} {
         assert_equal {point2 point1} [r geosearch points fromlonlat -179 37 bybox 400 400 km asc]
     }
 
+    test {GEOSEARCH with small distance} {
+        r del points
+        r geoadd points -122.407107 37.794300 1
+        r geoadd points -122.227336 37.794300 2
+        assert_equal {{1 0.0001} {2 9.8182}} [r GEORADIUS points -122.407107 37.794300 30 mi ASC WITHDIST]
+    }
+
     foreach {type} {byradius bybox} {
     test "GEOSEARCH fuzzy test - $type" {
         if {$::accurate} { set attempt 300 } else { set attempt 30 }