Fix build with Qt5.15.5

Index: src/KDb.cpp
--- src/KDb.cpp.orig
+++ src/KDb.cpp
@@ -1635,33 +1635,33 @@ QString KDb::escapeBLOB(const QByteArray& array, BLOBE
         for (int i = 0; i < size; i++) {
             const unsigned char val = array[i];
             if (val < 32 || val >= 127 || val == 39 || val == 92) {
-                str[new_length++] = '\\';
-                str[new_length++] = '\\';
-                str[new_length++] = '0' + val / 64;
-                str[new_length++] = '0' + (val % 64) / 8;
-                str[new_length++] = '0' + val % 8;
+                str[new_length++] = QLatin1Char('\\');
+                str[new_length++] = QLatin1Char('\\');
+                str[new_length++] = QChar::fromLatin1('0' + val / 64);
+                str[new_length++] = QChar::fromLatin1('0' + (val % 64) / 8);
+                str[new_length++] = QChar::fromLatin1('0' + val % 8);
             } else {
-                str[new_length++] = val;
+                str[new_length++] = QChar::fromLatin1(val);
             }
         }
     } else {
         for (int i = 0; i < size; i++) {
             const unsigned char val = array[i];
-            str[new_length++] = intToHexDigit(val / 16);
-            str[new_length++] = intToHexDigit(val % 16);
+            str[new_length++] =  QChar::fromLatin1(intToHexDigit(val / 16));
+            str[new_length++] =  QChar::fromLatin1(intToHexDigit(val % 16));
         }
     }
     if (type == BLOBEscapingType::XHex || type == BLOBEscapingType::Octal) {
-        str[new_length++] = '\'';
+        str[new_length++] = QLatin1Char('\'');
     } else if (type == BLOBEscapingType::ByteaHex) {
-        str[new_length++] = '\'';
-        str[new_length++] = ':';
-        str[new_length++] = ':';
-        str[new_length++] = 'b';
-        str[new_length++] = 'y';
-        str[new_length++] = 't';
-        str[new_length++] = 'e';
-        str[new_length++] = 'a';
+        str[new_length++] = QLatin1Char('\'');
+        str[new_length++] = QLatin1Char(':');
+        str[new_length++] = QLatin1Char(':');
+        str[new_length++] = QLatin1Char('b');
+        str[new_length++] = QLatin1Char('y');
+        str[new_length++] = QLatin1Char('t');
+        str[new_length++] = QLatin1Char('e');
+        str[new_length++] = QLatin1Char('a');
     }
     return str;
 }
